cht-bsw-rt5672: Add support for controlling speaker- and mic-mute LEDs

Add support for controlling speaker- and mic-mute LEDs using the new
snd_ctl_led kernel module for generic mute LED control.

Tested on a Thinkpad 10 tablet which has a detachable USB keyboard with
a speaker mute LED embedded in the volume-mute button and a mic mute
LED embedded in the mic-mute button.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>