Due to the conversion (drop) from 24bit in the DSP to 16bit in AC97,
the maximum capture level on Audigy seems lower than it could be.

This patch adds a workaround to enable the artificial capture boost
switch.  When this switch is on, the whole analog capature level is
boost up.  However, this results in the lower capture resolution.
Signed-off-by: Takashi Iwai <tiwai@suse.de>