ASoC: mediatek: add bindings for wm8960 codec machine driver

MT2701 with WM8960 CODEC

Required properties:

- compatible: "mediatek,mt2701-wm8960-machine"

- mediatek,platform: the phandle of MT2701 ASoC platform

- audio-routing: a list of the connections between audio

- mediatek,audio-codec: the phandles of wm8960 codec

- pinctrl-names: Should contain only one value - "default"

- pinctrl-0: Should specify pin control groups used for this controller.

Example:

	sound:sound {

		compatible = "mediatek,mt2701-wm8960-machine";

		mediatek,platform = <&afe>;

		audio-routing =

			"Headphone", "HP_L",

			"Headphone", "HP_R",

			"LINPUT1", "AMIC",

			"RINPUT1", "AMIC";

		mediatek,audio-codec = <&wm8960>;

		pinctrl-names = "default";

		pinctrl-0 = <&aud_pins_default>;

	};