hal: Use deep buffer output as primary

- The audio content in video clips, YouTube content, etc
  are being rendered through low latency path as it was
  set as default output profile. This results more power
  consumption for video playback.
- Fix this using deep buffer path as default one and use
  low latency path only for those audio tracks that
  request with AUDIO_OUTPUT_FLAG_FAST.

Change-Id: I52fafa0ec2a312bc4383c813497830e6ded071bc
CRs-Fixed: 570389

hal: Avoid duplicate primary outputs

open_output_stream API expects the default usecase to
be returned if other usecases are unavailable or unusable.
However, the output returned in this default case must be
the default primary if it exists.

 * cyanogen: This behavior is off by default.

Change-Id: Ie5cc53f077358d7039d62b09b29edb58c213bc08