An iommu domain is allocated in portal_set_cpu() and is attached to
pcfg->dev in the same function.

Use iommu_paging_domain_alloc() to make it explicit.
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20240610085555.88197-14-baolu.lu@linux.intel.comSigned-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>