android: boot: add vendor boot image to prepare for v3, v4 support

android: boot: add vendor boot image to prepare for v3, v4 support

Introduce vendor boot image for version 3 and 4 of boot image header.
The vendor boot image will hold extra information about kernel, dtb
and ramdisk.

This is done to prepare for boot image version 3 and 4 support.

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>