dt-bindings: interrupt-controller: Convert hisilicon,mbigen-v2 to DT schema

Convert the HiSilicon MBIGEN binding to DT schema format. It's a
straight-forward conversion.

Link: https://lore.kernel.org/r/20250812203327.730393-1-robh@kernel.org


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