Add HFP AIDL design am: e50be86fd4 am: fbf5d5c9d7 am: f410a9397b

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/2774933

Change-Id: Iabc0c6c62bc57e32bae66762a91bfdd95a9de895
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>