audiopolicy: make audio policy extensible

make function virtual or protected so that
they can be extended in custom audio policy.
Change-Id: Ida7992f6b327491fab1f4ea376e85e8eb34b89ca

audiopolicy: update APM to use custom audio policy configuration
Change-Id: I3161ff4fa41d37d0b761202f0b3a490d9c7e418e

audiopolicy: allow dp device selection for voice usecases
Change-Id: I13f1ddd0fd3655376d28a0ebe028d495fa2c6e5f

audiopolicy: follow-up change to support extended feature
Change-Id: Iddc14a3e2e61bc57f8637eae71e36cc21ce2d3e8

Change-Id: Ida7992f6b327491fab1f4ea376e85e8eb34b89ca