ALSA: intel8x0: Mute External Amplifier by default for ThinkPad X31

BugLink: https://bugs.launchpad.net/bugs/619439

This ThinkPad model needs External Amplifier muted for audible playback,
so set the inv_eapd quirk for it.

Reported-and-tested-by: Dennis Bell <dennis.bell@parkerg.co.uk>
Cc: <stable@kernel.org>
Signed-off-by: Daniel T Chen <crimsun@ubuntu.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
index 6433e65..4677492 100644
--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -1776,6 +1776,12 @@
         },
 	{
 		.subvendor = 0x1014,
+		.subdevice = 0x0534,
+		.name = "ThinkPad X31",
+		.type = AC97_TUNE_INV_EAPD
+	},
+	{
+		.subvendor = 0x1014,
 		.subdevice = 0x1f00,
 		.name = "MS-9128",
 		.type = AC97_TUNE_ALC_JACK