drm/i915: reject doubleclocked cea modes on dp

These are ultra-low-res modes used to upscale SDTV content and we
don't know how to support these on dp on intel hw:
- It's unclear whether we can send avi infoframes over dp ports.
- And the pixel repeat setting that work for hdmi/sdvo explicitly
  don't work for dp.

So don't bother and just reject these modes. These modes have been
introduced in

commit 54ac76f851a1789b047b74a8e14980f2dd1ac749
Author: Christian Schmidt <schmidt@digadd.de>
Date:   Mon Dec 19 14:53:16 2011 +0000

    drm/edid: support CEA video modes.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45729
Tested-by: Yuang Guang <guang.a.yang@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -266,6 +266,9 @@ intel_dp_mode_valid(struct drm_connector *connector,
 	if (mode->clock < 10000)
 		return MODE_CLOCK_LOW;
 
+	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
+		return MODE_H_ILLEGAL;
+
 	return MODE_OK;
 }
 
@@ -702,6 +705,9 @@ intel_dp_mode_fixup(struct drm_encoder *encoder, struct drm_display_mode *mode,
 		mode->clock = intel_dp->panel_fixed_mode->clock;
 	}
 
+	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
+		return false;
+
 	DRM_DEBUG_KMS("DP link computation with max lane count %i "
 		      "max bw %02x pixel clock %iKHz\n",
 		      max_lane_count, bws[max_clock], mode->clock);