leds: trigger: Introduce audio mute LED trigger

This patch adds a new LED trigger for coupling the audio mixer change
with the LED on laptops or other devices.  Currently there are two
trigger types, "audio-mute" and "audio-micmute".

The audio driver triggers the LED brightness change via
ledtrig_audio_set() call with the proper type (either mute or
mic-mute).  OTOH, the consumers may call ledtrig_audio_get() for the
initial brightness value that may have been set by the audio driver
beforehand.

This new stuff will be used by HD-audio codec driver and some platform
drivers (thinkpad_acpi and dell-laptop, also upcoming huawei-wmi).

Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

drivers/leds/trigger/Kconfig

@@ -136,4 +136,11 @@ config LEDS_TRIGGER_PATTERN
 	  which is a series of tuples, of brightness and duration (ms).
 	  If unsure, say N
 
+config LEDS_TRIGGER_AUDIO
+	tristate "Audio Mute LED Trigger"
+	help
+	  This allows LEDs to be controlled by audio drivers for following
+	  the audio mute and mic-mute changes.
+	  If unsure, say N
+
 endif # LEDS_TRIGGERS