audio: Fix for audio loss in FM and VR/A2DP concurrency

- Issue: VoiceRecgonition notification sound is
  not heard and there is audio loss in A2DP
  playback in VR/A2DP concurrency test cases.
  FM is not routing to BT when switched from
  Speaker.
- Rootcause: wrong device and usecase are used
  in AudioHardwareALSA::doRouting, the last item
  of mDeviceList is used blindly which contains
  wrong device/usecase.Audio HAL is overriding
  the active usecase based on the current output
  stream's usecase. But for FM an output stream
  won't be created. Hence Playback on BT is not
  started by audio HAL due to usecase mismatch.

- Fix: Add usecase as another input param in
  doRouting, and find matching device/usecase
  in mDeviceList before routing. Add check to
  avoid using output stream's usecase if FM is
  active.

Change-Id: Ic96373acba0ca94643f30040b5d9bf8cb87300c7
CRs-Fixed: 534424
CRs-Fixed: 532122