Merge "mkbootimg: support boot image version 4" am: a9333cb6ed am: bf97fc064c

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/1497378

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I21f37a03ee096a52ad3d6915398bb3e8d6d81768