drm/i915: Add limited color range readout for HDMI/DP ports on g4x/vlv/chv

The limited color range knob is in the port registers on
g4x and vlv/chv for HDMI, and on g4x for DP. Add the relevant code
to read out the hardware state into pipe config. On vlv/chv the
DP port limited color range knob is in PIPECONF for which we
already have readout code.

Cc: Chris Clayton <chris2553@googlemail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Chris Clayton <chris2553@googlemail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 81d7681f..fdff1d4 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1631,6 +1631,10 @@
 
 	pipe_config->adjusted_mode.flags |= flags;
 
+	if (!HAS_PCH_SPLIT(dev) && !IS_VALLEYVIEW(dev) &&
+	    tmp & DP_COLOR_RANGE_16_235)
+		pipe_config->limited_color_range = true;
+
 	pipe_config->has_dp_encoder = true;
 
 	intel_dp_get_m_n(crtc, pipe_config);