ASoC: tas6424: add bindings for TAS6424

Add the bindings for the TAS6424 digital amplifier.
Signed-off-by: Michael Stecklein <m-stecklein@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/ti,tas6424.txt

+Texas Instruments TAS6424 Quad-Channel Audio amplifier
+
+The TAS6424 serial control bus communicates through I2C protocols.
+
+Required properties:
+	- compatible: "ti,tas6424" - TAS6424
+	- reg: I2C slave address
+	- sound-dai-cells: must be equal to 0
+
+Example:
+
+tas6424: tas6424@6a {
+	compatible = "ti,tas6424";
+	reg = <0x6a>;
+
+	#sound-dai-cells = <0>;
+};
+
+For more product information please see the link below:
+http://www.ti.com/product/TAS6424-Q1