drm/i915: Always enable the cursor right after the primary plane

Follow the same sequence when enabling the cursor plane during
modeset. No point in doing this stuff in different order on different
generations.

This should also avoid a needless wait for vblank for the g4x cursor
workaround when the cursor gets enabled anyway.

Acked-by: Egbert Eich <eich@suse.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>