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)
- reg                  : Offset and length of the register set for the device
- 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)

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 H2 and M2)

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>;
		interrupts = <0 156 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&mstp0_clks R8A7791_CLK_MSIOF0>;
		#address-cells = <1>;
		#size-cells = <0>;
		status = "disabled";
	};
