iommu/amd: Store dev_data as device iommu private data

Do not use dev->archdata.iommu anymore and switch to using the private
per-device pointer provided by the IOMMU core code.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20200527115313.7426-10-joro@8bytes.org