msm8974: Re-add separate FAST device path

 * It seems all we needed is to OR deep buffer into the primary path
   to catch the stragglers.
 * This improves path selection for FAST tracks since error cases can
   be avoided when non-standard sample rates are used.

Change-Id: I7e9cc5df946d0cbe7e36c3fe0768b5ec7e47ed19