toradex: add support for u-boot update on colibri vf

Include flash scripts to boot partition, which can update u-boot
to NAND. Remove kernel and dtb files from boot partition, as they
are read from second partition.

u-boot env changed to boot from MMC by default and kernel
messages removed from tty1.

apalis flash scripts updated to latest version from toradex and
to use both flash_mmc and flash_blk.

Change-Id: I1a58badafa01e2023b9ae058b833eb108c097594
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@theqtcompany.com>