amd/iommu: assign iommu devices to Xen

amd/iommu: assign iommu devices to Xen

AMD IOMMU devices are exposed on the PCI bus, and thus are assigned by
default to the hardware domain. This can cause issues because the
IOMMU devices themselves are not behind an IOMMU, so update_paging_mode will
return an error if Xen tries to expand the page tables of a domain
that has assigned devices not behind an IOMMU. update_paging_mode
failing will cause the domain to be destroyed.

Fix this by hiding PCI IOMMU devices, so they are not assigned to the
hardware domain.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Brian Woods <brian.woods@amd.com>