galaxys2: Add audio.r_submix.default for casting

Source:
http://review.cyanogenmod.org/#/c/69238/  and
http://review.cyanogenmod.org/#/c/68962/

Change-Id: I787fab8378a607fc1381771f2ed748d7dbeb603a
Signed-off-by: zachd <runandhide05@gmail.com>