DT bindings for the R-Mobile/R-Car/RZ/G interrupt controller

Required properties:

- compatible: has to be "renesas,irqc-<soctype>", "renesas,irqc" as fallback.
  Examples with soctypes are:
    - "renesas,irqc-r8a73a4" (R-Mobile APE6)
    - "renesas,irqc-r8a7743" (RZ/G1M)
    - "renesas,irqc-r8a7745" (RZ/G1E)
    - "renesas,irqc-r8a77470" (RZ/G1C)
    - "renesas,irqc-r8a7790" (R-Car H2)
    - "renesas,irqc-r8a7791" (R-Car M2-W)
    - "renesas,irqc-r8a7792" (R-Car V2H)
    - "renesas,irqc-r8a7793" (R-Car M2-N)
    - "renesas,irqc-r8a7794" (R-Car E2)
    - "renesas,intc-ex-r8a774a1" (RZ/G2M)
    - "renesas,intc-ex-r8a774c0" (RZ/G2E)
    - "renesas,intc-ex-r8a7795" (R-Car H3)
    - "renesas,intc-ex-r8a7796" (R-Car M3-W)
    - "renesas,intc-ex-r8a77965" (R-Car M3-N)
    - "renesas,intc-ex-r8a77970" (R-Car V3M)
    - "renesas,intc-ex-r8a77980" (R-Car V3H)
    - "renesas,intc-ex-r8a77995" (R-Car D3)
- #interrupt-cells: has to be <2>: an interrupt index and flags, as defined in
  interrupts.txt in this directory
- clocks: Must contain a reference to the functional clock.

Optional properties:

- any properties, listed in interrupts.txt, and any standard resource allocation
  properties

Example:

	irqc0: interrupt-controller@e61c0000 {
		compatible = "renesas,irqc-r8a7790", "renesas,irqc";
		#interrupt-cells = <2>;
		interrupt-controller;
		reg = <0 0xe61c0000 0 0x200>;
		interrupts = <0 0 IRQ_TYPE_LEVEL_HIGH>,
			     <0 1 IRQ_TYPE_LEVEL_HIGH>,
			     <0 2 IRQ_TYPE_LEVEL_HIGH>,
			     <0 3 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&mstp4_clks R8A7790_CLK_IRQC>;
	};