drm: Extract drm_bridge.h

We don't want to burry the bridge structures kerneldoc in drm_crtc.h.

Cc: Archit Taneja <archit.taneja@gmail.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160831160913.12991-3-daniel.vetter@ffwll.ch
diff --git a/include/drm/drm_mode_object.h b/include/drm/drm_mode_object.h
index be3d938..43460b2 100644
--- a/include/drm/drm_mode_object.h
+++ b/include/drm/drm_mode_object.h
@@ -26,6 +26,7 @@
 #include <linux/kref.h>
 struct drm_object_properties;
 struct drm_property;
+struct drm_device;
 
 /**
  * struct drm_mode_object - base structure for modeset objects