Rockchip SRAM for pmu:
------------------------------

The sram of pmu is used to store the function of resume from maskrom(the 1st
level loader). This is a common use of the "pmu-sram" because it keeps power
even in low power states in the system.

Required node properties:
- compatible : should be "rockchip,rk3288-pmu-sram"
- reg : physical base address and the size of the registers window

Example:
	sram@ff720000 {
		compatible = "rockchip,rk3288-pmu-sram", "mmio-sram";
		reg = <0xff720000 0x1000>;
	};