Spreadtrum SoCs Watchdog timer

Required properties:
- compatible : Should be "sprd,sp9860-wdt".
- reg : Specifies base physical address and size of the registers.
- interrupts : Exactly one interrupt specifier.
- timeout-sec : Contain the default watchdog timeout in seconds.
- clock-names : Contain the input clock names.
- clocks : Phandles to input clocks.

Example:
	watchdog: watchdog@40310000 {
		compatible = "sprd,sp9860-wdt";
		reg = <0 0x40310000 0 0x1000>;
		interrupts = <GIC_SPI 61 IRQ_TYPE_LEVEL_HIGH>;
		timeout-sec = <12>;
		clock-names = "enable", "rtc_enable";
		clocks = <&clk_aon_apb_gates1 8>, <&clk_aon_apb_rtc_gates 9>;
	};
