Support certifying the boot.img in a boot-img.tar.gz am: 90a8372549 am: 3d88178cf6

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2109068

Change-Id: I99042305b4e8632d85893199351a8550b63850b0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>