MediaTek Idle States for cpuidle driver

ARM provides idle-state node to define the cpuidle states, as defined in [1].
cpuidle-mediatek is the cpuidle driver for MediaTek SoCs and uses these idle
states. Idle states have different enter/exit latency and residency values.

A cpu can power down and warmboot if there is a sufficient time between the
time it enters idle and the next known wake up. MediaTek idle-state is used
to indicate a core entering a power down state without consulting any other
cpu or the system resources. A core distinguishes itself in that the cpu
acknowledges and permits the SoC to enter deeper sleep modes. The MediaTek
Soc support suspend to idle state. This idle state will work efficiency when
platform will enter suspend. Supend to idle will have the same conservation
with system suspend in MediaTek SoC solution.


The idle-state for MediaTek SoCs are distinguished by the compatible property
of the idle-states device node.

The devicetree representation of the idle state should be -
Required properties:

- compatible: Must be one of -
	      "mediatek,idle-state",

Other required and optional properties are specified in [1].

Example:
	idle-states {
		entry-method = "arm,psci";

		cpuoff: cpuoff {
			compatible = "mediatek,idle-state";
			arm,psci-suspend-param = <0x00010001>;
			local-timer-stop;
			entry-latency-us = <50>;
			exit-latency-us = <100>;
			min-residency-us = <1400>;
		};

		clusteroff: clusteroff {
			compatible = "mediatek,idle-state";
			arm,psci-suspend-param = <0x01010001>;
			local-timer-stop;
			entry-latency-us = <50>;
			exit-latency-us = <100>;
			min-residency-us = <1400>;
		};

		mcusys: mcusys {
			compatible = "mediatek,idle-state";
			arm,psci-suspend-param = <0x01010002>;
			local-timer-stop;
			entry-latency-us = <150>;
			exit-latency-us = <200>;
			min-residency-us = <2000>;
		};

		s2idle: s2idle {
			compatible = "mediatek,idle-state";
			arm,psci-suspend-param = <0x01010100>;
			local-timer-stop;
			entry-latency-us = <0xffffffff>;
			exit-latency-us = <0xffffffff>;
			min-residency-us = <0xffffffff>;
		};
	};

[1]. Documentation/devicetree/bindings/arm/idle-states.txt