* Freescale MX233/MX28 SSP/SPI

Required properties:
- compatible: Should be "fsl,<soc>-spi", where soc is "imx23" or "imx28"
- reg: Offset and length of the register set for the device
- interrupts: Should contain SSP interrupts (error irq first, dma irq second)
- fsl,ssp-dma-channel: APBX DMA channel for the SSP

Example:

ssp0: ssp@80010000 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "fsl,imx28-spi";
	reg = <0x80010000 0x2000>;
	interrupts = <96 82>;
	fsl,ssp-dma-channel = <0>;
};

Add SSP/SPI device tree documentation
spi/mxs: Add SSP/SPI device tree documentation

Signed-off-by: Marek Vasut <f40600653b33f5282fa4c5daf377dfc444fb4625@denx.de>
Acked-by: Chris Ball <6ca7faee6ca9a094b1ee341f11b840a5608a8746@laptop.org>
Acked-by: Shawn Guo <912cf7eb7d8018e2943586ae6657d21fd4e38239@linaro.org>
Signed-off-by: Mark Brown <b51b9a92386687a9ac927cebfa0f978adeb8cea5@opensource.wolfsonmicro.com>
