Add audio module for remote submix

New definitions of audio devices for remote submix: one representing
  a sink for writing the audio buffers that won't be played directly
  locally, another representing the audio source that can be read from
  to obtain the audio mix.

New audio hardware module encapsulating the submix loop functionality.
  Create a Pipe to serve as non-blocking audio ring buffer between
  the output device (the sink) and the input device (the source).

Change-Id: I527f4721a69ced0430a99ebba3b4db7d419f2bb2
3 files changed