drm/i915: don't read HSW_AUD_PIN_ELD_CP_VLD when the power well is off

Because this will trigger "Unclaimed register" messages. All I need to
reproduce this problem is to boot my HSW machine with eDP+HDMI
connected.

Regression introduced by:

commit 9ed109a7b445e3f073d8ea72f888ec80c0532465
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Thu Apr 24 23:54:52 2014 +0200
    drm/i915: Track has_audio in the pipe config

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1560,9 +1560,11 @@ void intel_ddi_get_config(struct intel_encoder *encoder,
 		break;
 	}
 
-	temp = I915_READ(HSW_AUD_PIN_ELD_CP_VLD);
-	if (temp & (AUDIO_OUTPUT_ENABLE_A << (intel_crtc->pipe * 4)))
-		pipe_config->has_audio = true;
+	if (intel_display_power_enabled(dev_priv, POWER_DOMAIN_AUDIO)) {
+		temp = I915_READ(HSW_AUD_PIN_ELD_CP_VLD);
+		if (temp & (AUDIO_OUTPUT_ENABLE_A << (intel_crtc->pipe * 4)))
+			pipe_config->has_audio = true;
+	}
 
 	if (encoder->type == INTEL_OUTPUT_EDP && dev_priv->vbt.edp_bpp &&
 	    pipe_config->pipe_bpp > dev_priv->vbt.edp_bpp) {