drm/i915/display: rename CNL references in skl_scaler.c

With the removal of CNL, let's consider GLK as the first platform using
those constants since GLK has DISPLAY_VER == 10.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210728215946.1573015-16-lucas.demarchi@intel.com