Add simple support for this 8 channel volume control driver.
Currently all it does is to unmute all 8 channels.

Based upon Devin's initial patch made for an older kernel which I
cleaned up and rebased. Thanks to Kernel Labs for that work.
Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>