- this should actually change nothing at this point, just add capabilities
- the framework is implemented in lib/extensions.sh
- the "if function x exists then call x" replaced with call_extension_method()
  - +inline documentation
  - +compatibility names

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>

… gen

- 2 extensions dealing with extensibility itself
  - detect-unused-extensions: shows which extensions are enabled, but never called.
  - gen-sample-extension-docs: generates a sample empty extension & Markdown documentation for extensions

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>

- `SKIP_EXTERNAL_TOOLCHAINS=yes` - does not download or use any linaro toolchains, only build host-installed ones
- `SKIP_BOOTSPLASH=yes` - does not patch kernel for splash file
- `EXTRA_BSP_NAME=xyz` - allows for BSP variants, useful for when extensions modify the BSP
- `EXTRA_ROOTFS_MIB_SIZE=x` - add x mib's to rootfs size, for use with very small images
- `KERNEL_EXTRA_TARGETS` - what extra targets to make kernel for, default to "modules dtbs"
- `BOOTCONFIG=none` - does not build nor install u-boot; also doesn't handle bootscripts et al
- `unset KERNELSOURCE` - does not build nor install kernel, nor build initrd, nor build nor install firmware
- `ARMHF_ARCH=skip` - does not add armhf to apt/dpkg, thus pure arm64
- `SKIP_ARMBIAN_REPO=yes` - results in armbian.list.disabled in the final image
- define `APT_EXTRA_DIST_PARAMS` with apt-cacher-ng options and use it for `PACKAGE_LIST_INSTALL/REMOVE` et al
- initial support for targeting x86/amd64 UEFI and BIOS
    - some do's/don'ts for x86/amd64, like a different `UBUNTU_MIRROR` default
    - GPT/EFI(ESP) partitions (fat, `UEFISIZE=256` to enable, mount `UEFI_MOUNT_POINT=/boot/efi`, first on disk but ends
      up at `$uefipart`=15)
    - GPT/BIOS partitions (fat, `BIOSSIZE=1` to enable, second on disk but ends up at partition 14)
    - `UEFI_FS_LABEL="armbiefi"` - to set the FAT label for the EFI partition, visible in Win/Mac
    - hard-requires gdisk package host-side
- add add_host_dependencies() extension method; fill `EXTRA_BUILD_DEPS="pkg pkg2"` to install to host before toolchains
  download
- add pre_prepare_partitions() extension method, for custom partition size calculations
- add create_partition_table() extension method, used to do full-custom partitioning if `USE_HOOK_FOR_PARTITION=yes`
- add post_create_partitions() extension method, mostly for easy debugging
- add post_write_sdcard() extension method, where you can also set `SKIP_VERIFY=yes` to skip sdcard verification
- add post_install_kernel_debs() extension method.
- multiple fixes to bsp to avoid spurious errors when files are not where it expects
- v4: detect `update-initramfs` failure and abort build with useful message if it does
- v4: show useful stacktrace in `exit_with_error`
  - if `ERROR_DEBUG_SHELL=yes`, drop into a shell before unmounting/deleting everything, so we can inspect what went wrong
- v4: display a message before `apt-get remove PACKAGE_LIST_BOARD_REMOVE` packages, so any errors while removing are easy to understand
- v4: preserve kernel .config's dates when copying

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>

- a few examples of core refactoring using extensions
- sunxi-tools extension, enabled by 2 different sunxi family includes ("reuse" example)
- marvel-tools extension, enabled by 2 different mvebu family includes
- rkbin-tools extension, enabled by rockship64_common family include
- amlogic-fip/c2-blobs stuff refactored directly into meson64_common.inc ("single-use" example)
- removed the 'testings' fetch_from_repo completely since not used anywhere.

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>

- v3: added `growroot`-awareness to `armbian-resize-filesystem`
    - the partition-growing part of `armbian-resize-filesystem` does not deal correctly with the UEFI layout
    - `growroot` is installed on UEFI images by default, that handles growing partition during initramfs
    - now `armbian-resize-filesystem` handles `resize2fs` only, and works.
- v4: reworked UEFI board/family/include structure:
    - use Distro's `linux-generic` kernel only for `current`
    - `edge` now builds it's own pure-mainline `5.15.y` kernel, for both x86 and arm64
        - `.config` taken from Ubuntu, probably needs tuning for EXTRAWIFI=yes et al
- v4: introduce `SKIP_KERNEL_SYMLINK=yes`, tested in `builddeb`
    - to avoid symlinking kernel; u-boot likes it, but grub and flash-kernel hates it
- v5: many fixes
- v7: more small fixes.

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>

- this does not build it's own kernel "yet", but uses default linux-raspi kernel from Ubuntu
- flash-kernel is not really a bootloader
    - it just prepares kernel et al a FAT partition for booting by the RPi4b bootloader
    - flash-kernel is standard Debian package, but has only been tested on Ubuntu releases
- it is really only known-working since Hirsute release.
  - Debian's rpi kernel is armhf only, so out of scope here, at least until we add source-built kernels.
- v3: fixed focal rootfs build. untested.
- v3: better variable names, preparing for source-built kernel.
- v5: new edge build with pure mainline kernel.
- v6: many fixes and some hacks for packaging and layout, also firmware (using Ubuntu's)

Signed-off-by: Ricardo Pardini <ricardo@pardini.net>