dt-bindings: interrupt-controller: add Ralink SoCs interrupt controller

Add YAML doc for the interrupt controller which is present on Ralink SoCs.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20230623035901.1514341-1-sergio.paracuellos@gmail.com
Signed-off-by: Rob Herring <robh@kernel.org>