irqchip/gic-v3: Mark the base irq domain as DOMAIN_BUS_WIRED

As we're about to introduce MSI domains based on top of the GICv3
domain, we must make sure nothing the new domains do not alias
with the core domain.

So let's tag that core domain with the DOMAIN_BUS_WIRED attribute,
ensuring it gets picked up by other drivers that use irq_find_host().

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lkml.kernel.org/r/20180508121438.11301-7-marc.zyngier@arm.com