iommu/amd: Convert to using amd_io_pgtable

Make use of the new struct amd_io_pgtable in preparation to remove
the struct domain_pgtable.

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20201215073705.123786-5-suravee.suthikulpanit@amd.com


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