iommu/vt-d: Apply per-device dma_ops

Current Intel IOMMU driver sets the system level dma_ops. This causes
each dma API to go through the IOMMU driver even the devices are using
identity mapped domains. This sets per-device dma_ops only if a device
is using a DMA domain. Otherwise, use the default system level dma_ops
for direct dma.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Jon Derrick <jonathan.derrick@intel.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Link: https://lore.kernel.org/r/20200506015947.28662-4-baolu.lu@linux.intel.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>