Add defines for audio offload and non-blocking write

- Defines audio output flags for offloaded playback of compressed
    streams, and non-blocking HAL write()/drain()
- Adds audio_offload_info_t to pass additional information about a
    compressed stream when offloading

Change-Id: I4592d0877edd39e68d0c1035d0652adbd397bf3a
Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Signed-off-by: Eric Laurent <elaurent@google.com>