Spreadtrum pmic Watchdog timer

Required properties:
- compatible: should be one of following:
	"sprd,sc2723t-wdt",
	"sprd,sc2731-wdt",
	"sprd,sc2730-wdt",
	"sprd,sc2721-wdt",
	"sprd,sc2720-wdt",
	"sprd,ump9620-wdt",
- reg : Specifies base physical address and size of the registers.

Example:
	pmic_wdt: watchdog@40 {
			  compatible = "sprd,sc27xx-wdt", "sprd,sc2721-wdt";
			  reg = <0x40>;
	};
