use_mmio_flip() makes sure we only enable MMIO flips on gen5+. So we
don't need to take into account older devices.
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>