Marvell Orion SPI device

Required properties:
- compatible : should be on of the following:
    - "marvell,orion-spi" for the Orion, mv78x00, Kirkwood and Dove SoCs
    - "marvell,armada-370-spi", for the Armada 370 SoCs
    - "marvell,armada-375-spi", for the Armada 375 SoCs
    - "marvell,armada-380-spi", for the Armada 38x SoCs
    - "marvell,armada-390-spi", for the Armada 39x SoCs
    - "marvell,armada-xp-spi", for the Armada XP SoCs
- reg : offset and length of the register set for the device
- cell-index : Which of multiple SPI controllers is this.
Optional properties:
- interrupts : Is currently not used.

Example:
       spi@10600 {
	       compatible = "marvell,orion-spi";
	       #address-cells = <1>;
	       #size-cells = <0>;
	       cell-index = <0>;
	       reg = <0x10600 0x28>;
	       interrupts = <23>;
	       status = "disabled";
       };
