certify_bootimg: makes gki-info.txt optional am: 79627361ad am: 6236378e71 am: 8b855eb5f8 am: cade007f98

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2051402

Change-Id: I40b5b0aed09669e714cb6cfc1d00217d40923249
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>