iommu/arm-smmu: Do not access non-existing S2CR registers

The number of S2CR registers is not properly set when stream
matching is not supported. Fix this and add check that we do not try to
access outside of the number of S2CR regisrers.

Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
[will: added missing NUMSIDB_* definitions]
Signed-off-by: Will Deacon <will.deacon@arm.com>