build uboot from source, pull blobs from upstream, use dtbs from archive

[ogra1]

• drop all prebuilt bits
• build u-boot.bin from upstream source
• pull binary blobs from broadcoms upstream "stable" branch
• move config.txt and cmdline.txt to a configs subdir
• move uboot.patch and uboot.env.in to toplevel dir
• generate (and link) uboot.env during build
• pull devicetree files from the kernel package in the ubuntu archive
• update README

[kubiko]

two minor comments

[kubiko]

This could be simplified to once call:
ln -s uboot.env $SNAPCRAFT_PART_INSTALL/boot-assets/uboot.conf

[kubiko]

Don't you want to use tag instead of branch here, so we do not accidentally pick new version from upstream without prior testing?

[ogra1]

i'm not sure if --depth=1 works with tags, i have to try (the prob is without --depth=1 the checkkout takes between 30 and 45min because it pulls the whole history (vs a few seconds with --depth=1 )

[kubiko]

+1

[kubiko]

yep, uboot.env should be in top level
+1

[morphis]

Where does $arch come from?

[ogra1]

from coreutils (usually available on all build environments, but if you insist i can add it to build-packages as safety net)

note it is $(arch) ... i.e. the output of /usr/bin/arch ...

[morphis]

Thanks!

[morphis]

LGTM

[zyga]

Thanks for doing this @ogra1 -- I'm sorry to not have reviewed it earlier. Looks good.