ARM Freescale DSPI controller

Required properties:
- compatible : "fsl,vf610-dspi"
- reg : Offset and length of the register set for the device
- interrupts : Should contain SPI controller interrupt
- clocks: from common clock binding: handle to dspi clock.
- clock-names: from common clock binding: Shall be "dspi".
- pinctrl-0: pin control group to be used for this controller.
- pinctrl-names: must contain a "default" entry.
- spi-num-chipselects : the number of the chipselect signals.
- bus-num : the slave chip chipselect signal number.
- big-endian : if DSPI modudle is big endian, the bool will be set in node.
Example:

dspi0@4002c000 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "fsl,vf610-dspi";
	reg = <0x4002c000 0x1000>;
	interrupts = <0 67 0x04>;
	clocks = <&clks VF610_CLK_DSPI0>;
	clock-names = "dspi";
	spi-num-chipselects = <5>;
	bus-num = <0>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_dspi0_1>;
	big-endian;
	status = "okay";

	sflash: at26df081a@0 {
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "atmel,at26df081a";
		spi-max-frequency = <16000000>;
		spi-cpol;
		spi-cpha;
		reg = <0>;
		linux,modalias = "m25p80";
		modal = "at26df081a";
	};
};