drm/i915: Set PIPECONF color range bit on Valleyview

VLV has the color range selection bit in the PIPECONF register.
Configure it appropriately.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
[danvet: fixup rebase issues due to slightly different baseline.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>