ALSA: ice1712: Add S/PDIF suspend support for ICE1712-based M-Audio cards

Add S/PDIF suspend support for M-Audio cards based on ICE1712 chip.
Tested (playback only) on Audiophile 24/96. Capture will probably not work.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>