spi/davinci: add DT binding documentation

Davinci SPI controller device bindings

Required properties:

- #address-cells: number of cells required to define a chip select

	address on the SPI bus. Should be set to 1.

- #size-cells: should be zero.

- compatible:

	- "ti,dm6441-spi" for SPI used similar to that on DM644x SoC family

	- "ti,da830-spi" for SPI used similar to that on DA8xx SoC family

- reg: Offset and length of SPI controller register space

- num-cs: Number of chip selects

- ti,davinci-spi-intr-line: interrupt line used to connect the SPI

	IP to the interrupt controller within the SoC. Possible values

	are 0 and 1. Manual says one of the two possible interrupt

	lines can be tied to the interrupt controller. Set this

	based on a specifc SoC configuration.

- interrupts: interrupt number mapped to CPU.

- clocks: spi clk phandle

Example of a NOR flash slave device (n25q032) connected to DaVinci

SPI controller device over the SPI bus.

spi0:spi@20BF0000 {

	#address-cells			= <1>;

	#size-cells			= <0>;

	compatible			= "ti,dm6446-spi";

	reg				= <0x20BF0000 0x1000>;

	num-cs				= <4>;

	ti,davinci-spi-intr-line	= <0>;

	interrupts			= <338>;

	clocks				= <&clkspi>;

	flash: n25q032@0 {

		#address-cells = <1>;

		#size-cells = <1>;

		compatible = "st,m25p32";

		spi-max-frequency = <25000000>;

		reg = <0>;

		partition@0 {

			label = "u-boot-spl";

			reg = <0x0 0x80000>;

			read-only;

		};

		partition@1 {

			label = "test";

			reg = <0x80000 0x380000>;

		};

	};

};