[ALSA] ac97: YMF743 missing controls support (2/2)

These patches enable a few YMF743 controls (Tone/3D/IEC958) that won't
be detected with the current version of ALSA.
The second one contains following changes:
- A chip-specific SPDIF support for YMF743 (It doesn't have AC97
 standard SPDIF registers seen on YMF753).
- The implementation for 'IEC958 Playback Source' and 'IEC958 Mute'
 are identical to the ones for YMF753. But there is no 'IEC958 Output
 Pin' for YMF743.

Signed-off-by: Keita Maehara <maehara@debian.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>