ASoC: Add Odroid sound DT bindings documentation

This patch adds DT binding documentation for Odroid XU3/4
sound subsystem.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/samsung,odroid.txt

+Samsung Exynos Odroid XU3/XU4 audio complex with MAX98090 codec
+
+Required properties:
+
+ - compatible - "samsung,odroidxu3-audio" - for Odroid XU3 board,
+		"samsung,odroidxu4-audio" - for Odroid XU4 board
+ - model - the user-visible name of this sound complex
+ - 'cpu' subnode with a 'sound-dai' property containing the phandle of the I2S
+    controller
+ - 'codec' subnode with a 'sound-dai' property containing list of phandles
+    to the CODEC nodes, first entry must be corresponding to the MAX98090
+    CODEC and the second entry must be the phandle of the HDMI IP block node
+ - clocks - should contain entries matching clock names in the clock-names
+    property
+ - clock-names - should contain following entries:
+    - "epll" - indicating the EPLL output clock
+    - "i2s_rclk" - indicating the RCLK (root) clock of the I2S0 controller
+ - samsung,audio-widgets - this property specifies off-codec audio elements
+   like headphones or speakers, for details see widgets.txt
+ - 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 MAX98090's pins (as
+   documented in its binding), and the jacks on the board
+
+   For Odroid X2:
+     "Headphone Jack", "Mic Jack", "DMIC"
+
+   For Odroid U3, XU3:
+     "Headphone Jack", "Speakers"
+
+   For Odroid XU4:
+     no entries
+
+Example:
+
+sound {
+	compatible = "samsung,odroidxu3-audio";
+	samsung,cpu-dai = <&i2s0>;
+	samsung,codec-dai = <&max98090>;
+	model = "Odroid-XU3";
+	samsung,audio-routing =
+		"Headphone Jack", "HPL",
+		"Headphone Jack", "HPR",
+		"IN1", "Mic Jack",
+		"Mic Jack", "MICBIAS";
+
+	clocks = <&clock CLK_FOUT_EPLL>, <&i2s0 CLK_I2S_RCLK_SRC>;
+	clock-names = "epll", "sclk_i2s";
+
+	cpu {
+		sound-dai = <&i2s0 0>;
+	};
+	codec {
+		sound-dai = <&hdmi>, <&max98090>;
+	};
+};