drm/i915: DisplayPort hot remove notification to audio driver

On DP monitor hot remove, clear DP_AUDIO_OUTPUT_ENABLE accordingly, so that the audio driver will receive hot plug events and take action to refresh its device state and ELD contents.

Note that the DP_AUDIO_OUTPUT_ENABLE bit may be enabled or disabled only when the link training is complete and set to "Normal".

---
 drivers/gpu/drm/i915/intel_dp.c |    1 +
 1 file changed, 1 insertion(+)

This works both on KMS console and gnome desktop. Hot plug/unplug and DPMS on/off are all tested OK.

@@ -1771,6 +1771,7 @@ intel_dp_link_down(struct intel_dp *inte
 			intel_wait_for_vblank(dev, to_intel_crtc(crtc)->pipe);
 	}
 
+	DP &= ~DP_AUDIO_OUTPUT_ENABLE;
 	I915_WRITE(intel_dp->output_reg, DP & ~DP_PORT_EN);
 	POSTING_READ(intel_dp->output_reg);
 	msleep(intel_dp->panel_power_down_delay);