Freescale i.MX audio complex with SGTL5000 codec

Required properties:
- compatible : "fsl,imx-audio-sgtl5000"
- model : The user-visible name of this sound complex
- ssi-controller : The phandle of the i.MX SSI controller
- audio-codec : The phandle of the SGTL5000 audio codec
- 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,imx51-babbage-sgtl5000",
		     "fsl,imx-audio-sgtl5000";
	model = "imx51-babbage-sgtl5000";
	ssi-controller = <&ssi1>;
	audio-codec = <&sgtl5000>;
	mux-int-port = <1>;
	mux-ext-port = <3>;
};