ASoC: tfa9879: Add device tree bindings

Even though the tfa9879 driver can probe via device tree trough the
I2C core code, it is preferable to have explicit device tree
bindings instead [1], so add this support.

[1] https://www.spinics.net/lists/devicetree/msg195176.html

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Łukasz Majewski <lukma@denx.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/tfa9879.txt

@@ -0,0 +1,23 @@
+NXP TFA9879 class-D audio amplifier
+
+Required properties:
+
+- compatible : "nxp,tfa9879"
+
+- reg : the I2C address of the device
+
+Example:
+
+&i2c1 {
+	clock-frequency = <100000>;
+	pinctrl-names = "default";
+	pinctrl-0 = <&pinctrl_i2c1>;
+	status = "okay";
+
+	codec: tfa9879@6c {
+		#sound-dai-cells = <0>;
+		compatible = "nxp,tfa9879";
+		reg = <0x6c>;
+        };
+};
+

sound/soc/codecs/tfa9879.c

@@ -312,9 +312,15 @@ static const struct i2c_device_id tfa9879_i2c_id[] = {
 };
 MODULE_DEVICE_TABLE(i2c, tfa9879_i2c_id);
 
+static const struct of_device_id tfa9879_of_match[] = {
+	{ .compatible = "nxp,tfa9879", },
+	{ }
+};
+
 static struct i2c_driver tfa9879_i2c_driver = {
 	.driver = {
 		.name = "tfa9879",
+		.of_match_table = tfa9879_of_match,
 	},
 	.probe = tfa9879_i2c_probe,
 	.remove = tfa9879_i2c_remove,