Remove 'generic_ramdisk' and add 'boot' certification am: 3e4ce8371d am: 95809764cd am: 8e93e6f72e am: 0c42606c55

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

Change-Id: I7c31e8e6abcab811ca7842aa1657549e571b3934