Change audio flinger to user HAL master mute if available: DO NOT MERGE

Replicate the pattern used for HAL master volume support to make use
of master mute support if the HAL supports it.  This is part of the
change needed to address bug 6828363.  Because of the divergences
between ICS and master, this change will need to be merged by hand.

Signed-off-by: John Grossman <johngro@google.com>
Change-Id: I6d83be524021d273d093bcb117b8f2fe57c23685