PCI: Mark AMD Stoney Radeon R7 GPU ATS as broken

ATS is broken on the Radeon R7 GPU (at least for Stoney Ridge based laptop)
and causes IOMMU stalls and system failure.  Disable ATS on these devices
to make them usable again with IOMMU enabled.

Thanks to Joerg Roedel <jroedel@suse.de> for help.

[bhelgaas: In the email thread mentioned below, Alex suspects the real
problem is in sbios or iommu, so it may affect only certain systems, and it
may affect other devices in those systems as well.  However, per Joerg we
lack the ability to debug further, so this quirk is the best we can do for
now.]

Link: https://bugzilla.kernel.org/show_bug.cgi?id=194521
Link: https://lore.kernel.org/lkml/20190408103725.30426-1-nickel@altlinux.org
Fixes: 9b44b0b09d ("PCI: Mark AMD Stoney GPU ATS as broken")
Signed-off-by: Nikolai Kostrigin <nickel@altlinux.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
CC: stable@vger.kernel.org

drivers/pci/quirks.c

@@ -4903,6 +4903,7 @@ static void quirk_no_ats(struct pci_dev *pdev)
 
 /* AMD Stoney platform GPU */
 DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATI, 0x98e4, quirk_no_ats);
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_ATI, 0x6900, quirk_no_ats);
 #endif /* CONFIG_PCI_ATS */
 
 /* Freescale PCIe doesn't support MSI in RC mode */