Makefile is missing show how to usage correct parameters

[leonelhs]

BR-OpenIPC usage:

• make help|usage - print this help
• make install-deps - install system deps
• make prepare - download and unpack buildroot
• make list-configs - show available hardware configs list
• make BOARD= board-info - write to stdout information about selected board
• make BOARD= all - build all needed for a board (toolchain, kernel and rootfs images)
• make overlayed-rootfs- ROOTFS_OVERLAYS=... - create rootfs image that contains original
• make clean - cleaning before reassembly
• make distclean - switching to the factory state
  Buildroot target dir overlayed by some custom layers.
  Example:
  make overlayed-rootfs-squashfs ROOTFS_OVERLAYS=./examples/echo_server/overlay/

wrong command as is shown:
make list-configs
ls: cannot access '/Users/myuser/openipc/firmware/br-ext-chip-/configs': No such file or directory

command needs set to platform argument to work properly:
make list-configs PLATFORM=anyka
unknown_unknown_ak3918ev200_openipc_defconfig

make PLATFORM=anyka BOARD=ak3918ev200 all
making ....

[viktorxda]

Makefile usage was improved with #787