Analog Devices AXI SPI Engine controller Device Tree Bindings

Required properties:
- compatible		: Must be "adi,axi-spi-engine-1.00.a""
- reg			: Physical base address and size of the register map.
- interrupts		: Property with a value describing the interrupt
			  number.
- clock-names		: List of input clock names - "s_axi_aclk", "spi_clk"
- clocks		: Clock phandles and specifiers (See clock bindings for
			  details on clock-names and clocks).
- #address-cells	: Must be <1>
- #size-cells		: Must be <0>

Optional subnodes:
	Subnodes are use to represent the SPI slave devices connected to the SPI
	master. They follow the generic SPI bindings as outlined in spi-bus.txt.

Example:

    spi@@44a00000 {
		compatible = "adi,axi-spi-engine-1.00.a";
		reg = <0x44a00000 0x1000>;
		interrupts = <0 56 4>;
		clocks = <&clkc 15 &clkc 15>;
		clock-names = "s_axi_aclk", "spi_clk";

		#address-cells = <1>;
		#size-cells = <0>;

		/* SPI devices */
    };
