ASoC: samsung: Add DT bindings documentation for TM2 sound subsystem

This patch adds DT binding documentation for Exnos5433 based TM2
and TM2E boards sound subsystem.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/samsung,tm2-audio.txt

+Samsung Exynos5433 TM2(E) audio complex with WM5110 codec
+
+Required properties:
+
+ - compatible		 : "samsung,tm2-audio"
+ - model		 : the user-visible name of this sound complex
+ - audio-codec		 : the phandle of the wm5110 audio codec node,
+			   as described in ../mfd/arizona.txt
+ - i2s-controller	 : the phandle of the I2S controller
+ - audio-amplifier	 : the phandle of the MAX98504 amplifier
+ - samsung,audio-routing : a list of the connections between audio components;
+			   each entry is a pair of strings, the first being the
+			   connection's sink, the second being the connection's
+			   source; valid names for sources and sinks are the
+			   WM5110's and MAX98504's pins and the jacks on the
+			   board: HP, SPK, Main Mic, Sub Mic, Third Mic,
+			   Headset Mic
+ - mic-bias-gpios	 : GPIO pin that enables the Main Mic bias regulator
+
+
+Example:
+
+sound {
+	compatible = "samsung,tm2-audio";
+	audio-codec = <&wm5110>;
+	i2s-controller = <&i2s0>;
+	audio-amplifier = <&max98504>;
+	mic-bias-gpios = <&gpr3 2 0>;
+	model = "wm5110";
+	samsung,audio-routing =
+		"HP", "HPOUT1L",
+		"HP", "HPOUT1R",
+		"SPK", "SPKOUT",
+		"SPKOUT", "HPOUT2L",
+		"SPKOUT", "HPOUT2R",
+		"Main Mic", "MICBIAS2",
+		"IN1R", "Main Mic";
+};