Freescale i.MX audio complex with si476x codec

Required properties:
- compatible : "fsl,imx-audio-si476x"
- model : The user-visible name of this sound complex
- ssi-controller : The phandle of the i.MX SSI controller

- mux-int-port : The internal port of the i.MX audio muxer (AUDMUX)
- mux-ext-port : The external port of the i.MX audio muxer

Note: The AUDMUX port numbering should start at 1, which is consistent with
hardware manual.

Example:

sound {
	compatible = "fsl,imx-audio-si476x",
		     "fsl,imx-tuner-si476x";
	model = "imx-radio-si476x";

	ssi-controller = <&ssi1>;
	mux-int-port = <2>;
	mux-ext-port = <5>;
};