audio: Disable sonification on digital USB outputs

 * We don't want to hear touch sounds on our badass USB DACs. Just
   play the damn music, please :)

Change-Id: I08b1c5d672d853fc7116c03cd77b8828881d3a5b
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_hardware_libhardware_legacy into cm-11.0