Serial Peripheral Interface on Cirrus Logic CL-PS71xx, EP72xx, EP73xx

Required properties
- #address-cells: must be <1>
- #size-cells: must be <0>
- compatible: should include "cirrus,ep7209-spi"
- reg: Address and length of one register range
- interrupts: one interrupt line
- clocks: One entry, refers to the SPI bus clock
- cs-gpios: Specifies the gpio pins to be used for chipselects.
	    See: Documentation/devicetree/bindings/spi/spi-bus.txt

An additional register is present in the system controller,
which is assumed to be in the same device tree, with and marked
as compatible with "cirrus,ep7209-syscon3".

Example:

spi@80000500 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "cirrus,ep7209-spi";
	reg = <0x80000500 0x4>;
	interrupts = <15>;
	clocks = <&clks CLPS711X_CLK_SPI>;
};

syscon3: syscon@80002200 {
	compatible = "cirrus,ep7209-syscon3", "syscon";
	reg = <0x80002200 0x40>;
};

