certify_bootimg: support --extra_footer_args am: f754a7c3b8 am: a86f4ddbf6 am: 12bcad6963

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2104149

Change-Id: I273630ff11c4eddefa18f37f9c426a95d39b1831
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>