Remove 'generic_ramdisk' and add 'boot' certification am: 3e4ce8371d am: 95809764cd am: 8e93e6f72e am: 0c42606c55 am: d84ca9d806

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

Change-Id: Ia86fcc42fcad083ef718c2dda7aafaae5b9054f7