AudioTrack: support ENCODING_IEC61937 Set DIRECT flag. Use audio_has_proportional_frames() instead of audio_is_linear_pcm() where appropriate. Bug: 24541671 Bug: 20891646 Bug: 26373761 Change-Id: Ia32036b18683b084d6c9887593df87397ea0afd9 Signed-off-by: Phil Burk <philburk@google.com>