The map_sg callback is missing from arm_smmu_ops, but is required by
iommu.h. Similarly to most other IOMMU drivers, connect it to
default_iommu_map_sg.

Cc: <stable@vger.kernel.org>
Signed-off-by: NJean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>