iommu: Only log strictness for DMA domains

When passthrough is enabled, the default strictness policy becomes
irrelevant, since any subsequent runtime override to a DMA domain type
now embodies an explicit choice of strictness as well. Save on noise by
only logging the default policy when it is meaningfully in effect.

Reviewed-by: John Garry <john.garry@huawei.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/9d2bcba880c6d517d0751ed8bd4960853030b4d7.1628682049.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>