bootstd: Add test for Android boot image v2

bootstd: Add test for Android boot image v2

Rename actual android bootmethod test to specify it's for boot image
version 4.
Add a unit test for testing the Android bootmethod with boot image
version 2.

This requires another mmc image (mmc8) to contain the following
partitions:
- misc: contains the Bootloader Control Block (BCB)
- boot_a: contains a fake generic kernel image

we can test this with:

$ ./test/py/test.py --bd sandbox --build -k test_ut # build the mmc8.img
$ ./test/py/test.py --bd sandbox --build -k bootflow_android

Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Guillaume La Roque <glaroque@baylibre.com>
Link: https://lore.kernel.org/r/20241126-adnroidv2-v4-5-11636106dc69@baylibre.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>