drm/i915: check the power well inside haswell_get_pipe_config

This fixes "unclaimed register" messages when booting with eDP only
and i915.disable_power_well=1.

The error messages were caused by:

  commit 0e8ffe1b
  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>

drivers/gpu/drm/i915/intel_display.c

@@ -5978,9 +5978,14 @@ static bool haswell_get_pipe_config(struct intel_crtc *crtc,
 {
 	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;