drm/core: Preserve the framebuffer after removing it.

Previously RMFB and fd close chose to disable any plane that had
an active framebuffer from this file. If it was a primary plane the
crtc was disabled. However the fbdev code or any system compositor
should restore the planes anyway so there's no need to do it twice.

The old fb_id is zero'd, so there's no danger of being able to
restore the fb from fb_id.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -3327,7 +3327,7 @@ int drm_mode_rmfb(struct drm_device *dev,
 	mutex_unlock(&dev->mode_config.fb_lock);
 	mutex_unlock(&file_priv->fbs_lock);
 
-	drm_framebuffer_remove(fb);
+	drm_framebuffer_unreference(fb);
 
 	return 0;
 
@@ -3517,7 +3517,7 @@ void drm_fb_release(struct drm_file *priv)
 		list_del_init(&fb->filp_head);
 
 		/* This will also drop the fpriv->fbs reference. */
-		drm_framebuffer_remove(fb);
+		drm_framebuffer_unreference(fb);
 	}
 }