Add method in AudioManager to control remote submix through
AudioService.
AudioService controls remote submxi: enabling/disabling
remote submix will:
- make the sink audio device available/unavailable
- make the audio source available/unavailable
- force/unforce media streams to be routed to WFD
Change-Id: I05d9cc7c3e8a720318ec1385737cbd46a21a3207