[ALSA] ice1724 - Add functionality for Audiotrak Prodigy 7.1 LT

This patch adds support for useable front audio channels,
user controllable headphone channel and optical output.
From: Anho Ki
Signed-off-by: Matt Taylor <mwtaylor@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>