iommu/amd: Do not allocate io_pgtable_ops for passthrough domain

In passthrough mode we do not use IOMMU page table. Hence we don't need
to allocate io_pgtable_ops.

Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20230105091728.42469-1-vasant.hegde@amd.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>