Sigma Designs SMP86xx/SMP87xx watchdog

Required properties:
- compatible: Should be "sigma,smp8642-wdt"
- reg: Specifies the physical address region
- clocks: Should be a phandle to the clock

Optional properties:
- timeout-sec: watchdog timeout in seconds

Example:

watchdog@1fd00 {
	compatible = "sigma,smp8642-wdt";
	reg = <0x1fd00 8>;
	clocks = <&xtal_in_clk>;
	timeout-sec = <30>;
};