android: boot: support vendor boot image in abootimg

android: boot: support vendor boot image in abootimg

Vendor boot image is introduced in boot image header
version 3 and 4. Please check [1] for more details.

To prepare for boot image v3/v4 support, allow the abootimg command
to store the vendor_boot image address.

Full support for this new format will be done in a future patch.

Link:[1] https://source.android.com/docs/core/architecture/bootloader/partitions/vendor-boot-partitions

Signed-off-by: Safae Ouajih <souajih@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>