android: boot: add boot image header v3 and v4 structures

android: boot: add boot image header v3 and v4 structures

Add support for v3/v4 boot image format by adding
the following structures:

- andr_boot_img_hdr_v3 : describes boot image header
- andr_vnd_boot_img_hdr : describes vendor boot image header

These definitions have been copied over from the AOSP documentation at
[1] and [2]

Boot arg sizes are taken from [3]:
commit: 35fb6262bc3f (ANDROID: Support for vendor boot)

This also adds documentation for boot image header v3/v4 structure
that was imported from [4], file: include/bootimg/bootimg.h
commit: 8d0922bfb932 (Adding GKI signature in boot.img v4)

Link:[1] https://source.android.com/docs/core/architecture/bootloader/boot-image-header
Link:[2] https://source.android.com/docs/core/architecture/bootloader/partitions/vendor-boot-partitions#vendor-boot-header
Link:[3] https://android.googlesource.com/platform/external/u-boot
Link:[4] https://android.googlesource.com/platform/system/tools/mkbootimg

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>