[ALSA] MC97 modem mixer in sound/pci/ac97

AC97 Codec
Simple MC97 modem mixer with two common controls: Off-hook and CID,
and Si3056 MC specific control: Modem Speaker.

Signed-off-by: Sasha Khapyorsky <sashak@smlink.com>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>