drm/i915/chv: Add CHV display support

Add support for the third pipe in cherrview

v2: Don't use spaces for indentation (Jani)
    Wrap long lines

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Rafael Barbalho <rafael.barbalho@intel.com>
[vsyrjala: slightly massaged the patch]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>