ASoC: rt5631: Add device tree binding documentation

Document the device tree binding for the ALC5631 codec and update vendor
specific prefix for the Realtek.
Signed-off-by: Krishna Mohan Dani <krishna.md@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rt5631.txt

+ALC5631/RT5631 audio CODEC
+
+This device supports I2C only.
+
+Required properties:
+
+  - compatible : "realtek,alc5631" or "realtek,rt5631"
+
+  - reg : the I2C address of the device.
+
+Pins on the device (for linking into audio routes):
+
+  * SPK_OUT_R_P
+  * SPK_OUT_R_N
+  * SPK_OUT_L_P
+  * SPK_OUT_L_N
+  * HP_OUT_L
+  * HP_OUT_R
+  * AUX_OUT2_LP
+  * AUX_OUT2_RN
+  * AUX_OUT1_LP
+  * AUX_OUT1_RN
+  * AUX_IN_L_JD
+  * AUX_IN_R_JD
+  * MONO_IN_P
+  * MONO_IN_N
+  * MIC1_P
+  * MIC1_N
+  * MIC2_P
+  * MIC2_N
+  * MONO_OUT_P
+  * MONO_OUT_N
+  * MICBIAS1
+  * MICBIAS2
+
+Example:
+
+alc5631: alc5631@1a {
+	compatible = "realtek,alc5631";
+	reg = <0x1a>;
+};
+
+or
+
+rt5631: rt5631@1a {
+	compatible = "realtek,rt5631";
+	reg = <0x1a>;
+};