ASoC: Add Odroid sound DT bindings documentation

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>;

	};

};