KVM: arm64: GICv3: mandate page-aligned GICV region

KVM: arm64: GICv3: mandate page-aligned GICV region

Just like GICv2 was fixed in 63afbe7a0ac1
(kvm: arm64: vgic: fix hyp panic with 64k pages on juno platform),
mandate the GICV region to be both aligned on a page boundary and
its size to be a multiple of page size.

This prevents a guest from being able to poke at regions where we
have no idea what is sitting there.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
(cherry picked from commit fb3ec67942e92e5713e05b7691b277d0a0c0575d)
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>