drm/radeon: call hpd_irq_event on resume

BugLink: http://bugs.launchpad.net/bugs/1553179

commit dbb17a21 upstream.

Need to call this on resume if displays changes during
suspend in order to properly be notified of changes.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/radeon/radeon_device.c

@@ -1744,6 +1744,7 @@ int radeon_resume_kms(struct drm_device *dev, bool resume, bool fbcon)
 	}
 
 	drm_kms_helper_poll_enable(dev);
+	drm_helper_hpd_irq_event(dev);
 
 	/* set the power state here in case we are a PX system or headless */
 	if ((rdev->pm.pm_method == PM_METHOD_DPM) && rdev->pm.dpm_enabled)