audiopolicy: Add missing AV_ENHANCEMENTS flag

 * Fix all the audio :(

Change-Id: If41e2b2f1cba1c0ed24ef6ae06f9ede78081d834
audioflinger: Bind new mixer code to the resampler property

Don't try to use the new mixer mode if af.resampler.quality is set,
since they're incompatible. It's recommended that devices switch
by dropping the property though.

Change-Id: I18179799361108776a3a1e051bc0e23cd480fa10