certify_bootimg: support --gki_info for a boot.img am: 3886f4a68b am: 7b180d21cb am: c99a5c5da9 am: ee45f9a153 am: a09ceaeaa1

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

Change-Id: I4bc37e62c6529a14291a21cfc60df278aed52621
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>