* SPI (Serial Peripheral Interface)

Required properties:
- cell-index : SPI controller index.
- compatible : should be "fsl,spi".
- mode : the SPI operation mode, it can be "cpu" or "cpu-qe".
- reg : Offset and length of the register set for the device
- interrupts : <a b> where a is the interrupt number and b is a
  field that represents an encoding of the sense and level
  information for the interrupt.  This should be encoded based on
  the information in section 2) depending on the type of interrupt
  controller you have.
- interrupt-parent : the phandle for the interrupt controller that
  services interrupts for this device.

Optional properties:
- gpios : specifies the gpio pins to be used for chipselects.
  The gpios will be referred to as reg = <index> in the SPI child nodes.
  If unspecified, a single SPI device without a chip select can be used.

Example:
	spi@4c0 {
		cell-index = <0>;
		compatible = "fsl,spi";
		reg = <4c0 40>;
		interrupts = <82 0>;
		interrupt-parent = <700>;
		mode = "cpu";
		gpios = <&gpio 18 1	// device reg=<0>
			 &gpio 19 1>;	// device reg=<1>
	};