dt-bindings: riscv: cpus: Add missing additionalProperties on interrupt-controller node

The "interrupt-controller" CPU child node is missing constraints on
extra properties. Add "additionalProperties: false" to fix this.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230915201946.4184468-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>