iommu/amd: Return the pte page-size in fetch_pte

Extend the fetch_pte function to also return the page-size
that is mapped by the returned pte.

Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>