dt-bindings: interrupt-controller: ti,sci-intr: Fix missing reg property in the binding

Fix the following warning in dtbs_check
interrupt-controller@a00000: Unevaluated properties are not allowed ('reg' was unexpected)

Add the reg property in the schema.

Signed-off-by: Apurva Nandan <a-nandan@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220819190729.32358-4-a-nandan@ti.com