Add mkbootfs to build-tools am: 05274b3a78 am: f6ddf78da2 am: 9f0781e904 am: 7acf87f3e0

Original change: https://android-review.googlesource.com/c/platform/prebuilts/build-tools/+/1688282

Change-Id: Ifd5ea5f1733f9edf5f49e3b2ecaa8f545c1da550