Renesas MSIOF spi controller

Required properties:
- compatible           : "renesas,msiof-<soctype>" for SoCs,
			 "renesas,sh-msiof" for SuperH, or
			 "renesas,sh-mobile-msiof" for SH Mobile series.
			 Examples with soctypes are:
			 "renesas,msiof-r8a7790" (R-Car H2)
			 "renesas,msiof-r8a7791" (R-Car M2-W)
			 "renesas,msiof-r8a7792" (R-Car V2H)
			 "renesas,msiof-r8a7793" (R-Car M2-N)
			 "renesas,msiof-r8a7794" (R-Car E2)
- reg                  : A list of offsets and lengths of the register sets for
			 the device.
			 If only one register set is present, it is to be used
			 by both the CPU and the DMA engine.
			 If two register sets are present, the first is to be
			 used by the CPU, and the second is to be used by the
			 DMA engine.
- interrupt-parent     : The phandle for the interrupt controller that
			 services interrupts for this device
- interrupts           : Interrupt specifier
- #address-cells       : Must be <1>
- #size-cells          : Must be <0>

Optional properties:
- clocks               : Must contain a reference to the functional clock.
- num-cs               : Total number of chip-selects (default is 1)
- dmas                 : Must contain a list of two references to DMA
			 specifiers, one for transmission, and one for
			 reception.
- dma-names            : Must contain a list of two DMA names, "tx" and "rx".

Optional properties, deprecated for soctype-specific bindings:
- renesas,tx-fifo-size : Overrides the default tx fifo size given in words
			 (default is 64)
- renesas,rx-fifo-size : Overrides the default rx fifo size given in words
			 (default is 64, or 256 on R-Car Gen2)

Pinctrl properties might be needed, too.  See
Documentation/devicetree/bindings/pinctrl/renesas,*.

Example:

	msiof0: spi@e6e20000 {
		compatible = "renesas,msiof-r8a7791";
		reg = <0 0xe6e20000 0 0x0064>, <0 0xe7e20000 0 0x0064>;
		interrupts = <0 156 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&mstp0_clks R8A7791_CLK_MSIOF0>;
		dmas = <&dmac0 0x51>, <&dmac0 0x52>;
		dma-names = "tx", "rx";
		#address-cells = <1>;
		#size-cells = <0>;
		status = "disabled";
	};
