legacy/alsa_sound: Fix for a crash in Audio Policy Service

- isStreamActiveRemotely is missing in audio policy module
  This is resulting in a crash when this call is made on
  AudioPolicyService.
- Fix is to implement this method in audio policy hal so that
  the call is routed to audio policy manager

CRs-Fixed: 508811

Change-Id: I3b4bb723ea5bbc25cb39b12fa06743873465a144