dt-bindings: soc: Add documentation for the MediaTek SCPSYS unit

MediaTek SCPSYS

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

The System Control Processor System (SCPSYS) has several power management

related tasks in the system. The tasks include thermal measurement, dynamic

voltage frequency scaling (DVFS), interrupt filter and lowlevel sleep control.

The System Power Manager (SPM) inside the SCPSYS is for the MTCMOS power

domain control.

The driver implements the Generic PM domain bindings described in

power/power_domain.txt. It provides the power domains defined in

include/dt-bindings/power/mt8173-power.h.

Required properties:

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

- #power-domain-cells: Must be 1

- reg: Address range of the SCPSYS unit

- infracfg: must contain a phandle to the infracfg controller

- clock, clock-names: clocks according to the common clock binding.

                      The clocks needed "mm" and "mfg". These are the

		      clocks which hardware needs to be enabled before

		      enabling certain power domains.

Example:

	scpsys: scpsys@10006000 {

		#power-domain-cells = <1>;

		compatible = "mediatek,mt8173-scpsys";

		reg = <0 0x10006000 0 0x1000>;

		infracfg = <&infracfg>;

		clocks = <&clk26m>,

			 <&topckgen CLK_TOP_MM_SEL>;

		clock-names = "mfg", "mm";

	};

Example consumer:

	afe: mt8173-afe-pcm@11220000 {

		compatible = "mediatek,mt8173-afe-pcm";

		power-domains = <&scpsys MT8173_POWER_DOMAIN_AUDIO>;

	};