AMD IOMMU: allocate IRTE entries instead of using a static mapping

AMD IOMMU: allocate IRTE entries instead of using a static mapping

For multi-vector MSI, where we surely don't want to allocate
contiguous vectors and be able to set affinities of the individual
vectors separately, we need to drop the use of the tuple of vector and
delivery mode to determine the IRTE to use, and instead allocate IRTEs
(which imo should have been done from the beginning).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>