Allwinner SoCs Watchdog timer

Required properties:

- compatible : should be one of
	"allwinner,sun4i-a10-wdt"
	"allwinner,sun6i-a31-wdt"
	"allwinner,sun50i-a64-wdt","allwinner,sun6i-a31-wdt"
- reg : Specifies base physical address and size of the registers.

Example:

wdt: watchdog@1c20c90 {
	compatible = "allwinner,sun4i-a10-wdt";
	reg = <0x01c20c90 0x10>;
};