drm/i915: Avoid circular locking from intel_fbdev_fini()

lockdep spots that the fb_info->lock takes the dev->struct_mutex during
init (due to the device probing) and so we can not hold
dev->struct_mutex when unregistering the framebuffer. Simply reverse the
order of initialisation during cleanup and so do the intel_fbdev_fini()
before the intel_modeset_cleanup.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_dma.c

@@ -2106,6 +2106,7 @@ int i915_driver_unload(struct drm_device *dev)
 	acpi_video_unregister();
 
 	if (drm_core_check_feature(dev, DRIVER_MODESET)) {
+		intel_fbdev_fini(dev);
 		intel_modeset_cleanup(dev);
 
 		/*

drivers/gpu/drm/i915/intel_display.c

@@ -6130,8 +6130,6 @@ void intel_modeset_cleanup(struct drm_device *dev)
 	drm_kms_helper_poll_fini(dev);
 	mutex_lock(&dev->struct_mutex);
 
-	intel_fbdev_fini(dev);
-
 	list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) {
 		/* Skip inactive CRTCs */
 		if (!crtc->fb)

drivers/gpu/drm/i915/intel_fb.c

@@ -206,8 +206,8 @@ static struct drm_fb_helper_funcs intel_fb_helper_funcs = {
 	.fb_probe = intel_fb_find_or_create_single,
 };
 
-static int intel_fbdev_destroy(struct drm_device *dev,
-			       struct intel_fbdev *ifbdev)
+static void intel_fbdev_destroy(struct drm_device *dev,
+				struct intel_fbdev *ifbdev)
 {
 	struct fb_info *info;
 	struct intel_framebuffer *ifb = &ifbdev->ifb;
@@ -225,9 +225,7 @@ static int intel_fbdev_destroy(struct drm_device *dev,
 
 	drm_framebuffer_cleanup(&ifb->base);
 	if (ifb->obj)
-		drm_gem_object_unreference(ifb->obj);
-
-	return 0;
+		drm_gem_object_unreference_unlocked(ifb->obj);
 }
 
 int intel_fbdev_init(struct drm_device *dev)