AMD IOMMU: handle MSI for phantom functions

AMD IOMMU: handle MSI for phantom functions

With ordinary requests allowed to come from phantom functions, the
remapping tables ought to be set up to also allow for MSI triggers to
come from other than the "real" device too.

It is not clear to me whether the alias-ID handling also needs
adjustment for this to work properly, or whether firmware can be
expected to properly express this through a device alias range
descriptor (or multiple device alias ones).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>