[ALSA] ca0106: Add analog mute controls for cards with SPI DAC

Add four mute controls for the analog output channels for cards that use
an SPI DAC, like the SB0570 SB Live! 24-bit / Audigy SE.  The Wolfson DAC
doesn't support muting left/right so the controls are mono.
The chip state struct gets a 32-byte array to act as a shadow of the spi
dac registers.  Only two registers are used for mute, but more would be
needed for analog gain, de-emphasis, DAC power down, phase inversion, and
other features.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>