KVM: arm64: nv: Enforce S2 alignment when contiguous bit is set

Despite KVM not using the contiguous bit for anything related to
TLBs, the spec does require that the alignment defined by the
contiguous bit for the page size and the level is enforced.

Add the required checks to offset the point where PA and VA merge.

Fixes: 61e30b9e ("KVM: arm64: nv: Implement nested Stage-2 page table walk logic")
Reported-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>