hal: Featureize FLAC offload support

 * Not all devices will have this code in the DSP, let alone the kernel.
 * Featurize it, but leave the codec bit width and sample rate controls
   in place so that 24-bit PCM offload still works.
 * Enable by default.

Change-Id: I6e156048906a2b638e9ec4a083755536a14e161f