drm/xe/rtp: Add match helper for gslice fused off

drm/xe/rtp: Add match helper for gslice fused off

Add match helper to detect when the first gslice is fused off, as needed
by future workarounds.

v2:
  - Add warning if called on a platform without geometry pipeline
    (Matt Roper)
  - Hardcode 4 as the number of gslices, which matches all the currently
    supported platforms. PVC doesn't have geometry pipeline and
    shouldn't use this function (Matt Roper)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://lore.kernel.org/r/20230314003012.2600353-2-lucas.demarchi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>