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

Optional properties:
- num-cs : total number of chipselects
- 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)


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 : polling, interrupt or dma
- 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

