drm/xe/execlist: Log when using execlist submission

Make explicit in the log that execlist submission is used to prevent from
silently using it over GuC submission.

Signed-off-by: Francois Dugast <francois.dugast@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>