dt-bindings: interrupt-controller: arm,gic-v3: Add missing type to interrupt-partition-* nodes

Add missing 'type: object' schema to interrupt-partition-* nodes. Found
with fix to meta-schema checks.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>