I think you can take the dtsi file in the BSP for reference.
e.g. imx6qdl-sabresd.dtsi. mux-int-port and mux-ext-port is used to set the AUDMUX in/out port number.
under the :
sound {
compatible = "fsl,imx6q-sabresd-wm8962",
...
...
...
mux-int-port = <2>;
mux-ext-port = <3>;
For more details, please read the linux documentation. Documentation/devicetree/bindings/sound/imx-audio-wm8962.txt