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: NDennis Bell <dennis.bell@parkerg.co.uk>
Cc: <stable@kernel.org>
Signed-off-by: NDaniel T Chen <crimsun@ubuntu.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/pci/intel8x0.c

@@ -1774,6 +1774,12 @@ static struct ac97_quirk ac97_quirks[] __devinitdata = {
 		.name = "HP/Compaq nx7010",
 		.type = AC97_TUNE_MUTE_LED
         },
+	{
+		.subvendor = 0x1014,
+		.subdevice = 0x0534,
+		.name = "ThinkPad X31",
+		.type = AC97_TUNE_INV_EAPD
+	},
 	{
 		.subvendor = 0x1014,
 		.subdevice = 0x1f00,