This fixes "unclaimed register" messages when booting with eDP only
and i915.disable_power_well=1.
The error messages were caused by:
  commit 
0e8ffe1bf81b0780cc6229cb38664754dffe8776
  Author: Daniel Vetter <daniel.vetter@ffwll.ch>
  Date:   Thu Mar 28 10:42:00 2013 +0100
      drm/i915: add hw state readout/checking for pipe_config
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
 {
        struct drm_device *dev = crtc->base.dev;
        struct drm_i915_private *dev_priv = dev->dev_private;
+       enum transcoder cpu_transcoder = crtc->config.cpu_transcoder;
        uint32_t tmp;
 
-       tmp = I915_READ(PIPECONF(crtc->config.cpu_transcoder));
+       if (!intel_using_power_well(dev_priv->dev) &&
+           cpu_transcoder != TRANSCODER_EDP)
+               return false;
+
+       tmp = I915_READ(PIPECONF(cpu_transcoder));
        if (!(tmp & PIPECONF_ENABLE))
                return false;