drm/xe: Add mmio read before GGTT invalidate

drm/xe: Add mmio read before GGTT invalidate

On LNL without a mmio read before a GGTT invalidate the GuC can
incorrectly read the GGTT scratch page upon next access leading to jobs
not getting scheduled. A mmio read before a GGTT invalidate seems to fix
this. Since a GGTT invalidate is not a hot code path, blindly do a mmio
read before each GGTT invalidate.

Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: stable@vger.kernel.org
Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Reported-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3164
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241023221200.1797832-1-matthew.brost@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>