Disable/restore sprite planes around mode-set just like we do for the
primary and cursor planes. Now that we have working sprite clipping,
this actually works quite decently.

Previosuly we didn't even bother to disable sprites when changing mode,
which could lead to a corrupted sprite appearing on the screen after a
modeset (at least on my IVB). Not sure if all hardware generations would
be so forgiving when enabled sprites end up outside the pipe dimensons.

v2: Disable rather than enable sprites in ironlake_crtc_disable()
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>