iommu/arm-smmu: Use correct address mask for CMD_TLBI_S2_IPA

Stage-2 TLBI by IPA takes a 48-bit address field, as opposed to the
64-bit field used by the VA-based invalidation commands.

This patch re-jigs the SMMUv3 command construction code so that the
address field is correctly masked.

Signed-off-by: Will Deacon <will.deacon@arm.com>