Kleaf: add mkbootimg.py. am: cc9c13a21d am: da90cf07db am: 744b8b3263 am: 99cf7e8987

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/1760945

Change-Id: I51973209978fb4c0b8e281b653b2b62f67f693ea