hammerhead: Enable deep buffer output as primary

 * Since we're not offloading audio during AV playback, it's
   better to use DEEP_BUFFER as the primary output and only
   select the FAST output when the flag is set. This saves
   power during video playback.

Change-Id: I94d4de328377e9c351bd77c5ad5b0a7ec96cbb79