iommu/amd: Move Kconfig and Makefile bits down into amd directory

Move AMD Kconfig and Makefile bits down into the amd directory
with the rest of the AMD specific files.

Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20200630200636.48600-3-jsnitsel@redhat.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>