drm/i915: Disable atomics in L3 for gen9

drm/i915: Disable atomics in L3 for gen9

Enabling atomic operations in L3 leads to unrecoverable GPU hangs, as
the machine stops responding milliseconds after receipt of the reset
request [GDRT]. By disabling the cached atomics, the hang do not occur
and we presume the GPU would reset normally for similar hangs.

Sadly this is a shotgun approach, but since the impact is critical it is
better to err on the safe side and work back from there.

Reported-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110998
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jason Ekstrand <jason@jlekstrand.net>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Jason Ekstrand <jason@jlesktrand.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210125220152.24070-1-chris@chris-wilson.co.uk
Cc: stable@vger.kernel.org
(cherry picked from commit b267c7ae0ad5b437b068f46919b17f85000154b4)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>