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

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

Change-Id: I719b8987a8826452e7cca8401cb41a7d3290beff