Merge "Allow vendors to add custom vbmeta partitions" am: b80d9d6c

Original change: https://android-review.googlesource.com/c/platform/build/+/2380861



Change-Id: Id38f4980039b9cefb9c0f3f5f215588ae59867b5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>