dt-bindings: interrupt-controller: Convert brcm,bcm6345-l1-intc to DT schema

dt-bindings: interrupt-controller: Convert brcm,bcm6345-l1-intc to DT schema

Convert the Broadcom BCM6345 interrupt controller binding to schema
format.

The old schema indicated SoC specific compatibles should be present, but
there are none in use. So drop them.

The most number of CPUs on any platform seems to be 2, so document that
as the maximum.

Link: https://lore.kernel.org/r/20250505144622.1287712-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>