Rockchip SFC Controller for SOC

Required properties:
- compatible : "rockchip,sfc".
- reg : shall contain registers location and length for data and reg.
- interrupts : shall define the nand controller interrupt.
- clocks : shall reference sfc controller clocks.
- clock-names : sfc controller internal clock names. Shall contain :
    * "clk_sfc" : sfc controller clock
    * "hclk_sfc" : sfc ahb clock gate
- assigned-clocks : sclk preset by dts
- assigned-clock-frequency : sclk frequency, io clk = sclk/2;

Examples:
sfc: sfc@301c0000 {
	compatible = "rockchip,sfc";
	reg = <0x301c0000 0x200>;
	interrupts = <GIC_SPI 56 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clk_sfc>, <&clk_gates15 10>;
	clock-names = "clk_sfc", "hclk_sfc";
	assigned-clocks = <&cru SCLK_SFC>;
	assigned-clock-frequency = <100000000>;
	status = "okay";
};