drm/i915: Kill intel_panel_fitter_pipe()

Check pipe config gmch_pfit.control instead of using intel_panel_fitter_pipe()
to figure out if the pipe for the overlay is using the panel fitter.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1481131693-27993-7-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>