IMG Synchronous Peripheral Flash Interface (SPFI) controller

Required properties:
- compatible: Must be "img,spfi".
- reg: Must contain the base address and length of the SPFI registers.
- interrupts: Must contain the SPFI interrupt.
- clocks: Must contain an entry for each entry in clock-names.
  See ../clock/clock-bindings.txt for details.
- clock-names: Must include the following entries:
  - spfi: SPI operating clock
  - sys: SPI system interface clock
- dmas: Must contain an entry for each entry in dma-names.
  See ../dma/dma.txt for details.
- dma-names: Must include the following entries:
  - rx
  - tx
- cs-gpios: Must specify the GPIOs used for chipselect lines.
- #address-cells: Must be 1.
- #size-cells: Must be 0.

Optional properties:
- img,supports-quad-mode: Should be set if the interface supports quad mode
  SPI transfers.
- spfi-max-frequency: Maximum speed supported by the spfi block.

Example:

spi@18100f00 {
	compatible = "img,spfi";
	reg = <0x18100f00 0x100>;
	interrupts = <GIC_SHARED 22 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&spi_clk>, <&system_clk>;
	clock-names = "spfi", "sys";
	dmas = <&mdc 9 0xffffffff 0>, <&mdc 10 0xffffffff 0>;
	dma-names = "rx", "tx";

	#address-cells = <1>;
	#size-cells = <0>;
};
