iommu/amd: Properly account for virtual aliases in IOMMU groups

An alias doesn't always point to a physical device.  When this
happens we must first verify that the IOMMU group isn't rooted in
a device above the alias.  In this case the alias is effectively
just another quirk for the devices aliased to it.  Alternatively,
the virtual alias itself may be the root of the IOMMU group.  To
support this, allow a group to be hosted on the alias dev_data
for use by anything that might have the same alias.

Signed-off-by: Alex williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>