Add a new flag, auto_mute_via_amp, to determine the behavior of the
headphone / line-out auto-mute.  When this flag is set, the generic
driver mutes the speaker and line outputs via the amp mute of each
pin, instead of changing the pin control values.

This is introduced for devices that don't work expectedly with the pin
control values; for example, some devices are known to keep enabling
the speaker outputs no matter which pin control values are set on the
speaker pins.

The driver doesn't check actually whether the pins have the output amp
caps, but assumes that the proper mixer (mute) controls are created on
all these pins.  If not the case, you can't use this flag for your
device.

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