ec/lenovo/h8: Fix mute LEDs

thinkpad_acpi expects a SSMS method to turn on/off the mute LED
and a MMTS method to turn on/off the microphone mute LED. With
these methods implemented the driver can correctly sync the LEDs
with the corresponding statuses.

There seems to be two different bits to mute the audio in the
Lenovo H8 EC:
 * AMUT, used internally (for example to disable the audio before
    entering S3).
 * ALMT, controllable by the OS, which also toggles the mute LED
    (if present).

Tested on a X220T and on a X201.

Change-Id: I578f95f9619a53fd35f8a8bfe5564aeb6c789212
Signed-off-by: Nicola Corna <nicola@corna.info>
Reviewed-on: https://review.coreboot.org/18329
Reviewed-by: Alexander Couzens <lynxis@fe80.eu>
Tested-by: build bot (Jenkins)

src/ec/lenovo/h8/acpi/ec.asl

@@ -39,8 +39,11 @@ Device(EC)
 				DKR2, 1,	/* Dock register 2 */
 		Offset (0x2a),
 				EVNT, 8,	/* write will trigger EC event */
+		Offset (0x30),
+				    , 6,
+				ALMT, 1,	/* Audio Mute + LED */
 		Offset (0x3a),
-				AMUT, 1,	/* Audio Mute */
+				AMUT, 1,	/* Audio Mute (internal use) */
 				    , 3,
 				BTEB, 1,
 				WLEB, 1,
@@ -362,6 +365,23 @@ Device(EC)
 		{
 			Return (TBSW << 3)
 		}
+		/* Mute audio */
+		Method (SSMS, 1, NotSerialized)
+		{
+			Store(Arg0, ALMT)
+		}
+		/* Control mute microphone LED */
+		Method (MMTS, 1, NotSerialized)
+		{
+			If (Arg0)
+			{
+				TLED(0x8E)
+			}
+			Else
+			{
+				TLED(0x0E)
+			}
+		}
 		/* Version */
 		Method (MHKV, 0, NotSerialized)
 		{