PCI: Mark AMD Stoney GPU ATS as broken

ATS is broken on this hardware and causes IOMMU stalls and system failure.
Disable ATS on these devices to make them usable again with IOMMU enabled.

Note that the commit in the Fixes tag is not buggy; it just uncovers the
problem in the hardware by increasing the ATS flush rate.

Link: https://lists.linuxfoundation.org/pipermail/iommu/2017-March/020836.html
Link: https://bugzilla.redhat.com/show_bug.cgi?id=1409201
Fixes: b1516a14

 ("iommu/amd: Implement flush queue")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>