To account for parts of the chip that are "harvested" (disabled) due to
silicon flaws, caches on some AMD GPUs must be initialized before ATS is
enabled.

ATS is normally enabled by the IOMMU driver before the GPU driver loads, so
this cache initialization would have to be done in a quirk, but that's too
complex to be practical.

For Navi14 (device ID 0x7340), this initialization is done by the VBIOS,
but apparently some boards went to production with an older VBIOS that
doesn't do it.  Disable ATS for those boards.

Link: https://lore.kernel.org/r/20200114205523.1054271-3-alexander.deucher@amd.com
Bug: https://gitlab.freedesktop.org/drm/amd/issues/1015
See-also: d28ca864 ("PCI: Mark AMD Stoney Radeon R7 GPU ATS as broken")
See-also: 9b44b0b0 ("PCI: Mark AMD Stoney GPU ATS as broken")
[bhelgaas: squash into one patch, simplify slightly, commit log]
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org