DT bindings for the R-/SH-Mobile irqpin controller

Required properties:

- compatible: has to be "renesas,intc-irqpin-<soctype>", "renesas,intc-irqpin"
  as fallback.
  Examples with soctypes are:
    - "renesas,intc-irqpin-r8a7740" (R-Mobile A1)
    - "renesas,intc-irqpin-r8a7778" (R-Car M1A)
    - "renesas,intc-irqpin-r8a7779" (R-Car H1)
    - "renesas,intc-irqpin-sh73a0" (SH-Mobile AG5)

- reg: Base address and length of each register bank used by the external
  IRQ pins driven by the interrupt controller hardware module. The base
  addresses, length and number of required register banks varies with soctype.

- #interrupt-cells: has to be <2>: an interrupt index and flags, as defined in
  interrupts.txt in this directory

Optional properties:

- any properties, listed in interrupts.txt, and any standard resource allocation
  properties
- sense-bitfield-width: width of a single sense bitfield in the SENSE register,
  if different from the default 4 bits
- control-parent: disable and enable interrupts on the parent interrupt
  controller, needed for some broken implementations
