On IVB the display data buffer partitioning control lives in the
DISP_ARB_CTL2 register. Add the relevant defines/code for it.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>