Synchronize UsbAlsaDevice, rename playback/capture.

Synchronize external access to UsbAlsaDevice fields.
Rename all playback fields to output, capture to input.
Move Alsa Device String generation to UsbAlsaDevice.

Test: Used Google Play Music to test audio output while
inserting & removing USB audio devices.

Bug: 68337205
Bug: 70632415
Change-Id: I77d413736253e28a33993f45e6e405209563f3e4