Add support for controlling remote submix audio routing

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