[ALSA] Improve the shared-jack handling on ac97

AC97 Codec
The handling of shared surround/clfe output jacks with line/mic-in
on some AC97 codecs is improved.

Instead of 'Line-In As Surround' or 'Mic As Center/LFE' switch, two
new enum controls are introduced: 'Channel Mode' and 'Surround Jack Mode'.
The formar changes the current output mode among 2, 4 and 6-channels.
The latter controls whether the jacks are shared or independent.

Signed-off-by: Takashi Iwai <tiwai@suse.de>