ASoC: Add device tree binding for WM8731

Tested with the famous "hey, look! this compiles" test plan.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>
Acked by: Grant Likely <grant.likely@secretlab.ca>

Documentation/devicetree/bindings/sound/wm8731.txt

+WM8731 audio CODEC
+
+This device supports both I2C and SPI (configured with pin strapping
+on the board).
+
+Required properties:
+
+  - compatible : "wlf,wm8731"
+
+  - reg : the I2C address of the device for I2C, the chip select
+          number for SPI.
+
+Example:
+
+codec: wm8731@1a {
+	compatible = "wlf,wm8731";
+	reg = <0x1a>;
+};

sound/soc/codecs/wm8731.c

@@ -22,6 +22,7 @@
 #include <linux/platform_device.h>
 #include <linux/regulator/consumer.h>
 #include <linux/spi/spi.h>
+#include <linux/of_device.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>
@@ -607,6 +608,13 @@ static struct snd_soc_codec_driver soc_codec_dev_wm8731 = {
 	.num_dapm_routes = ARRAY_SIZE(wm8731_intercon),
 };
 
+static const struct of_device_id wm8731_of_match[] = {
+	{ .compatible = "wlf,wm8731", },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(of, wm8731_of_match);
+
 #if defined(CONFIG_SPI_MASTER)
 static int __devinit wm8731_spi_probe(struct spi_device *spi)
 {
@@ -638,6 +646,7 @@ static struct spi_driver wm8731_spi_driver = {
 	.driver = {
 		.name	= "wm8731",
 		.owner	= THIS_MODULE,
+		.of_match_table = wm8731_of_match,
 	},
 	.probe		= wm8731_spi_probe,
 	.remove		= __devexit_p(wm8731_spi_remove),
@@ -682,6 +691,7 @@ static struct i2c_driver wm8731_i2c_driver = {
 	.driver = {
 		.name = "wm8731",
 		.owner = THIS_MODULE,
+		.of_match_table = wm8731_of_match,
 	},
 	.probe =    wm8731_i2c_probe,
 	.remove =   __devexit_p(wm8731_i2c_remove),