drm/i915: Drain freed object after suspend display

Display is turned off by i915_drm_suspend() during the suspend
procedure, removing the last reference of some gem objects that were
used by display.

The issue is that those objects are only actually freed when
mm.free_work executed and that can happen very late in the suspend
process causing issues.
So here draining all freed objects released by display fixing suspend
issues.
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220629134721.48375-1-jose.souza@intel.com

drivers/gpu/drm/i915/i915_driver.c

@@ -1163,6 +1163,8 @@ static int i915_drm_suspend(struct drm_device *dev)
 
 	enable_rpm_wakeref_asserts(&dev_priv->runtime_pm);
 
+	i915_gem_drain_freed_objects(dev_priv);
+
 	return 0;
 }