dt-bindings: MediaTek: Add binding document for the AUXADC

MediaTek AUXADC

===============

The Auxiliary Analog/Digital Converter (AUXADC) is an ADC found

in some Mediatek SoCs which among other things measures the temperatures

in the SoC. It can be used directly with register accesses, but it is also

used by thermal controller which reads the temperatures from the AUXADC

directly via its own bus interface. See

Documentation/devicetree/bindings/thermal/mediatek-thermal.txt

for the Thermal Controller which holds a phandle to the AUXADC.

Required properties:

- compatible: Must be "mediatek,mt8173-auxadc"

- reg: Address range of the AUXADC unit

Example:

auxadc: auxadc@11001000 {

	compatible = "mediatek,mt8173-auxadc";

	reg = <0 0x11001000 0 0x1000>;

};