dt-bindings: interrupt-controller: Convert apm,xgene1-msi to DT schema

Convert the Applied Micro X-Gene MSI controller binding to DT schema
format. MSI controllers go in interrupt-controller directory so move the
schema there.

Link: https://lore.kernel.org/r/20250710180757.2970583-1-robh@kernel.org


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