Add HFP AIDL design am: e50be86fd4 am: 2d5b69bab5 am: 4716916bcb

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

Change-Id: Iae5d6b304a5dbd3493e901653b35c959a6d3463b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>