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".

Tested OK for both hot plug/remove and DPMS on/off.
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1926,6 +1926,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
 			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);