dt-bindings: thermal: Add binding document for Mediatek thermal controller

* Mediatek Thermal

This describes the device tree binding for the Mediatek thermal controller

which measures the on-SoC temperatures. This device does not have its own ADC,

instead it directly controls the AUXADC via AHB bus accesses. For this reason

this device needs phandles to the AUXADC. Also it controls a mux in the

apmixedsys register space via AHB bus accesses, so a phandle to the APMIXEDSYS

is also needed.

Required properties:

- compatible: "mediatek,mt8173-thermal"

- reg: Address range of the thermal controller

- interrupts: IRQ for the thermal controller

- clocks, clock-names: Clocks needed for the thermal controller. required

                       clocks are:

		       "therm":	 Main clock needed for register access

		       "auxadc": The AUXADC clock

- resets: Reference to the reset controller controlling the thermal controller.

- mediatek,auxadc: A phandle to the AUXADC which the thermal controller uses

- mediatek,apmixedsys: A phandle to the APMIXEDSYS controller.

- #thermal-sensor-cells : Should be 0. See ./thermal.txt for a description.

Optional properties:

- nvmem-cells: A phandle to the calibration data provided by a nvmem device. If

               unspecified default values shall be used.

- nvmem-cell-names: Should be "calibration-data"

Example:

	thermal: thermal@1100b000 {

		#thermal-sensor-cells = <1>;

		compatible = "mediatek,mt8173-thermal";

		reg = <0 0x1100b000 0 0x1000>;

		interrupts = <0 70 IRQ_TYPE_LEVEL_LOW>;

		clocks = <&pericfg CLK_PERI_THERM>, <&pericfg CLK_PERI_AUXADC>;

		clock-names = "therm", "auxadc";

		resets = <&pericfg MT8173_PERI_THERM_SW_RST>;

		reset-names = "therm";

		mediatek,auxadc = <&auxadc>;

		mediatek,apmixedsys = <&apmixedsys>;

		nvmem-cells = <&thermal_calibration_data>;

		nvmem-cell-names = "calibration-data";

	};