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

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

Change-Id: I62db328cf4260308e9cc227ef0f588d762ea4e4b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>