certify_bootimg: support --gki_info for a boot.img am: 3886f4a68b am: 7b180d21cb

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2079119

Change-Id: I3acac1ffdae2403e9734d0bb4a031c953eaf05ef
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>