Remove 'generic_ramdisk' and add 'boot' certification am: 3e4ce8371d am: 95809764cd am: 8e93e6f72e

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/1999090

Change-Id: I918942661bcb463f87ef9fdca6f596d49f1f4ac0