I had a request for a 4 channel mode.  This should implement front
and surround outputs, leaving the 3rd plug for mic input.
Signed-off-by: Tobin Davis <tdavis@dsl-only.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>