ASoC: Add device tree binding for WM8750

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>

Documentation/devicetree/bindings/sound/wm8750.txt

@@ -0,0 +1,18 @@
+WM8750 and WM8987 audio CODECs
+
+These devices support both I2C and SPI (configured with pin strapping
+on the board).
+
+Required properties:
+
+  - compatible : "wlf,wm8750" or "wlf,wm8987"
+
+  - reg : the I2C address of the device for I2C, the chip select
+          number for SPI.
+
+Example:
+
+codec: wm8750@1a {
+	compatible = "wlf,wm8750";
+	reg = <0x1a>;
+};