drm/i915: Enable DP audio for Haswell

This patch adds the missing code to send ELD for Haswell DisplayPort,
based on Xingchao's original patch.

A test was performed with HSW-D machine and NEC EA232Wmi DP monitor.

Cc: Xingchao Wang <xingchao.wang@intel.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -669,6 +669,15 @@ static void intel_ddi_mode_set(struct drm_encoder *encoder,
 			break;
 		}
 
+		if (intel_dp->has_audio) {
+			DRM_DEBUG_DRIVER("DP audio on pipe %c on DDI\n",
+					 pipe_name(intel_crtc->pipe));
+
+			/* write eld */
+			DRM_DEBUG_DRIVER("DP audio: write eld information\n");
+			intel_write_eld(encoder, adjusted_mode);
+		}
+
 		intel_dp_init_link_config(intel_dp);
 
 	} else if (type == INTEL_OUTPUT_HDMI) {