There are a few duplicated codes handling the mute and mic-mute LEDs
via GPIO pins.  Let's consolidate to single helpers.  Here we
introduced two new fields to alc_spec, gpio_mute_led_mask and
gpio_mic_led_mask, to contain the bit mask to set/clear.  Also,
mute_led_polarity is evaluated as well.
Signed-off-by: NTakashi Iwai <tiwai@suse.de>