UNISOC Poweroff Driver

This IP block in the unisoc SoC that only deals with different ways to power the system down.

Required properties:
- compatible:
  -"sprd,sc27xx-poweroff" for SC27xx poweroff
  -"sprd,ump9620-poweroff" for UMP9620 poweroff
- reg: Specifies the physical address of the poweroff register.

Example:
poweroff@1820 {
	compatible = "sprd,sc27xx-poweroff", "sprd,sc2730-poweroff";
	reg = <0x1820>;
};
