dt-bindings: interrupt-controller: arm,gic: Fix schema errors in example

Validating the examples against the schema have a few errors:

arm,gic.example.dt.yaml: 'ranges' does not match any of the regexes: '^v2m@[0-9a-f]+$', 'pinctrl-[0-9]+'
arm,gic.example.dt.yaml: #address-cells:0:0: 2 is not one of [0, 1]
arm,gic.example.dt.yaml: #size-cells:0:0: 1 was expected

'ranges' is valid, but missing from the schema, so add it. The reg
addresses and sizes don't match the schema requirements and the example
template. We could just override the example template to use 64-bit
addresses, but there's not really any value showing that in the example.

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