iommu: make inclusion of arm/arm-smmu-v3 directory conditional

Nothing in there is active if CONFIG_ARM_SMMU_V3 is not enabled, so the whole
directory can depend on that switch as well.

Fixes: e86d1aa8 ("iommu/arm-smmu: Move Arm SMMU drivers into their own subdirectory")
Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/2434059.NG923GbCHz@devpool92.emlix.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>