Add HFP AIDL design am: e50be86fd4 am: 2d5b69bab5

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

Change-Id: I928e9685ba15b492401bed639bfd3aea00abd024
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>