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
Merge remote-tracking branch 'cyanogen/cm-12.0' into cm-12.0