iommu/vt-d: Prepare for multiple DMA domain types

In preparation for the strict vs. non-strict decision for DMA domains
to be expressed in the domain type, make sure we expose our flush queue
awareness by accepting the new domain type, and test the specific
feature flag where we want to identify DMA domains in general. The DMA
ops reset/setup can simply be made unconditional, since iommu-dma
already knows only to touch DMA domains.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/31a8ef868d593a2f3826a6a120edee81815375a7.1628682049.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>