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

Required properties:

- compatible: has to be "renesas,intc-irqpin"
- #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
