ARM PL022 SPI controller

Required properties:
- compatible : "arm,pl022", "arm,primecell"
- reg : Offset and length of the register set for the device
- interrupts : Should contain SPI controller interrupt
- num-cs : total number of chipselects

Optional properties:
- cs-gpios : should specify GPIOs 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.
- pl022,autosuspend-delay : delay in ms following transfer completion before
			    the runtime power management system suspends the
			    device. A setting of 0 indicates no delay and the
                            device will be suspended immediately
- pl022,rt : indicates the controller should run the message pump with realtime
             priority to minimise the transfer latency on the bus (boolean)
- dmas : Two or more DMA channel specifiers following the convention outlined
         in bindings/dma/dma.txt
- dma-names: Names for the dma channels, if present. There must be at
	     least one channel named "tx" for transmit and named "rx" for
             receive.


SPI slave nodes must be children of the SPI master node and can
contain the following properties.

- pl022,interface : interface type:
	0: SPI
	1: Texas Instruments Synchronous Serial Frame Format
	2: Microwire (Half Duplex)
- pl022,com-mode : specifies the transfer mode:
	0: interrupt mode
	1: polling mode (default mode if property not present)
	2: DMA mode
- pl022,rx-level-trig : Rx FIFO watermark level
- pl022,tx-level-trig : Tx FIFO watermark level
- pl022,ctrl-len : Microwire interface: Control length
- pl022,wait-state : Microwire interface: Wait state
- pl022,duplex : Microwire interface: Full/Half duplex


Example:

	spi@e0100000 {
		compatible = "arm,pl022", "arm,primecell";
		reg = <0xe0100000 0x1000>;
		#address-cells = <1>;
		#size-cells = <0>;
		interrupts = <0 31 0x4>;
		dmas = <&dma-controller 23 1>,
			<&dma-controller 24 0>;
		dma-names = "rx", "tx";

		m25p80@1 {
			compatible = "st,m25p80";
			reg = <1>;
			spi-max-frequency = <12000000>;
			spi-cpol;
			spi-cpha;
			pl022,interface = <0>;
			pl022,com-mode = <0x2>;
			pl022,rx-level-trig = <0>;
			pl022,tx-level-trig = <0>;
			pl022,ctrl-len = <0x11>;
			pl022,wait-state = <0>;
			pl022,duplex = <0>;
		};
	};