iommu/arm-smmu: Support v7s context format

Fill in the last bits of machinery required to drive a stage 1 context
bank in v7 short descriptor format. By default we'll prefer to use it
only when the CPUs are also using the same format, such that we're
guaranteed that everything will be strictly 32-bit.

Change-Id: I49925ef37271707338ee84f179ac6bc6cb8289e5
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Git-commit: 6070529b
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm-4.4


Signed-off-by: Patrick Daly <pdaly@codeaurora.org>