Documentation: Define the MOP500 Audio Machine Driver Device Tree bindings

Here we add the required documentation for the new Device Tree
bindings pertaining to the MOP500 Audio Machine driver.
Acked-by: NOla Lilja <ola.o.lilja@stericsson.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/sound/ux500-mop500.txt

+* MOP500 Audio Machine Driver
+
+This node is responsible for linking together all ux500 Audio Driver components.
+
+Required properties:
+ - compatible              : "stericsson,snd-soc-mop500"
+
+Non-standard properties:
+ - stericsson,cpu-dai      : Phandle to the CPU-side DAI
+ - stericsson,audio-codec  : Phandle to the Audio CODEC
+ - stericsson,card-name    : Over-ride default card name
+
+Example:
+
+	sound {
+		compatible = "stericsson,snd-soc-mop500";
+
+		stericsson,cpu-dai = <&msp1 &msp3>;
+		stericsson,audio-codec = <&codec>;
+	};
+
+	msp1: msp@80124000 {
+		compatible = "stericsson,ux500-msp-i2s";
+		reg = <0x80124000 0x1000>;
+		interrupts = <0 62 0x4>;
+		v-ape-supply = <&db8500_vape_reg>;
+	};
+
+	msp3: msp@80125000 {
+		compatible = "stericsson,ux500-msp-i2s";
+		reg = <0x80125000 0x1000>;
+		interrupts = <0 62 0x4>;
+		v-ape-supply = <&db8500_vape_reg>;
+	};
+
+	codec: ab8500-codec {
+		compatible = "stericsson,ab8500-codec";
+		stericsson,earpeice-cmv = <950>; /* Units in mV. */
+	};