colibri_vf: add update_uboot wrapper

Add universal update_uboot wrapper that helps to update
U-Boot image on internal storage.

Usage example:
> tftpboot ${loadaddr} ${board_name}/u-boot-nand.imx
> run update_uboot

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
1 file changed