usbaudio: Make the USB audio HAL actually work.

 * Set a default device if none is set.
 * Shush some logging.
 * Only use the mmap interface on QCOM devices.

Change-Id: I790a6733e85b169e645e020fa92608a0d4fea3c2
usbaudio: Provide a way to hardcode the card id

 * Some devices will have secondary sound cards for things like SPDIF.
 * Let's provide a way to hardcode the correct value for now until we
   have framework support for doing this correctly.

Change-Id: I6f3396692f1acc1602491e3a3befea8e04b6c9cf