manta: Enable switch device for USB audio

 * When a USB audio device is connected, flip the switch so that userspace
   knows about it.

Change-Id: I47bd5e487656dd1c404c11d12e4abd50bcd9d61d
cm: manta: Enable USB audio stack

Change-Id: I79be22fb1a1158aa42d1e46ff6d2e54e4115e237