* Realtek rts39xx spi nor flash controller

Required properties/subnode:
- compatible: Should be "realtek,rts3903-quadspi"
- reg: Address and length of the register set for the device
- interrupt-parent: Phandle of the parent interrupt controller
- interrupts: Should contain sdio controller interrupt
- clocks : Clock specifiers
- clock-names : identifier string for clock specifiers
- swp_enable : enable software write protection

Example:
	spi0: spic@0x18030000 {
		compatible = "realtek,rts3903-quadspi";
		#address-cells = <1>;
		#size-cells = <0>;
		reg = <0x18030000 0x10000>;
		clocks = <&clks RLX_CLK_BUS_CK>;
		clock-names = "spi_ck";
		spi-max-frequency = <60000000>;
		interrupt-parent = <&cpuintc>;
		interrupts = <BSP_IRQ_SPI>;
		swp_enable;
	};
