iommu/s390: Tolerate repeat attach_dev calls

Since commit 0286300e

 ("iommu: iommu_group_claim_dma_owner() must
always assign a domain") s390-iommu will get called to allocate multiple
unmanaged iommu domains for a vfio-pci device -- however the current
s390-iommu logic tolerates only one.  Recognize that multiple domains can
be allocated and handle switching between DMA or different iommu domain
tables during attach_dev.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20220519182929.581898-1-mjrosato@linux.ibm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>