iommu/arm-smmu-v3: Report IOMMU_CAP_ENFORCE_CACHE_COHERENCY for CANWBS

HW with CANWBS is always cache coherent and ignores PCI No Snoop requests
as well. This meets the requirement for IOMMU_CAP_ENFORCE_CACHE_COHERENCY,
so let's return it.

Implement the enforce_cache_coherency() op to reject attaching devices
that don't have CANWBS.

Reviewed-by: Nicolin Chen <[email protected]>
Reviewed-by: Mostafa Saleh <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Reviewed-by: Jerry Snitselaar <[email protected]>
Reviewed-by: Donald Dutile <[email protected]>
Tested-by: Nicolin Chen <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

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