ALSA: hda/sigmatel: fix S/PDIF out on Intel D*45* motherboards

ALSA: hda/sigmatel: fix S/PDIF out on Intel D*45* motherboards

The BIOS botches this one completely - it says the 2nd S/PDIF output is
used, while in fact it's the 1st one. This is tested on DP45SG, but I'm
assuming it's valid for the other boards in the series as well.

Also add some comments regarding the pins.
FWIW, the codec is apparently still sold by Tempo Semiconductor, Inc.,
where one can download the documentation.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20230405201220.2197826-2-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>