Add subscribe to VHAL proto. am: 5c846f7cc9

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3096234

Change-Id: I69fa802d59a0b5ac45bb8a5e541a9ef7a8d43fc2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>