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>

drivers/iommu/arm-smmu-v3.c

@@ -3336,13 +3336,11 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 	}
 
 	/* Boolean feature flags */
-#if 0	/* ATS invalidation is slow and broken */
 	if (IS_ENABLED(CONFIG_PCI_PRI) && reg & IDR0_PRI)
 		smmu->features |= ARM_SMMU_FEAT_PRI;
 
 	if (IS_ENABLED(CONFIG_PCI_ATS) && reg & IDR0_ATS)
 		smmu->features |= ARM_SMMU_FEAT_ATS;
-#endif
 
 	if (reg & IDR0_SEV)
 		smmu->features |= ARM_SMMU_FEAT_SEV;