Revert "iommu/arm-smmu-v3: Disable detection of ATS and PRI"

This reverts commit b5e86196.

Now that ATC invalidation is performed in the correct places and without
incurring a locking overhead for non-ATS systems, we can re-enable the
corresponding SMMU feature detection.

Signed-off-by: Will Deacon <will@kernel.org>