On CTG and IVB+ we don't try to preserve any bits from the
DPFC_CONTROL register. Follow suit on ILK/SNB.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>