Synopsys DesignWare SPI master

Required properties:
- compatible: should be "snps,designware-spi"
- #address-cells: see spi-bus.txt
- #size-cells: see spi-bus.txt
- reg: address and length of the spi master registers
- interrupts: should contain one interrupt
- clocks: spi clock phandle
- num-cs: see spi-bus.txt

Optional properties:
- cs-gpios: see spi-bus.txt

Example:

spi: spi@4020a000 {
	compatible = "snps,designware-spi";
	interrupts = <11 1>;
	reg = <0x4020a000 0x1000>;
	clocks = <&pclk>;
	num-cs = <2>;
	cs-gpios = <&banka 0 0>;
};
