iommu/arm-smmu: Support SMMUv1 64KB supplement

The 64KB Translation Granule Supplement to the SMMUv1 architecture
allows an SMMUv1 implementation to support 64KB pages for stage 2
translations, using a constrained VMSAv8 descriptor format limited
to 40-bit addresses. Now that we can freely mix and match context
formats, we can actually handle having 4KB pages via an AArch32
context but 64KB pages via an AArch64 context, so plumb it in.

It is assumed that any implementations will have hardware capabilities
matching the format constraints, thus obviating the need for excessive
sanity-checking; this is the case for MMU-401, the only ARM Ltd.
implementation.

CC: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>