Freescale Digital Audio Mux (AUDMUX) device

Required properties:
- compatible : "fsl,imx21-audmux" for AUDMUX version firstly used on i.MX21,
  or "fsl,imx31-audmux" for the version firstly used on i.MX31.
- reg : Should contain AUDMUX registers location and length

An initial configuration can be setup using child nodes.

Required properties of optional child nodes:
- fsl,audmux-port : Integer of the audmux port that is configured by this
  child node.
- fsl,port-config : List of configuration options for the specific port. For
  imx31-audmux and above, it is a list of tuples <ptcr pdcr>. For
  imx21-audmux it is a list of pcr values.

Example:

audmux@021d8000 {
	compatible = "fsl,imx6q-audmux", "fsl,imx31-audmux";
	reg = <0x021d8000 0x4000>;
};