drm/gem: switch dev->object_name_lock to a mutex

I want to wrap the creation of a dma-buf from a gem object in it,
so that the obj->export_dma_buf cache can be atomically filled in.

Instead of creating a new mutex just for that variable I've figured
I can reuse the existing dev->object_name_lock, especially since
the new semantics will exactly mirror the flink obj->name already
protected by that lock.

v2: idr_preload/idr_preload_end is now an atomic section, so need to
move the mutex locking outside.

[airlied: fix up conflict with patch to make debugfs use lock]

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 7782dbb..bf05847 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1196,7 +1196,7 @@
 
 	/** \name GEM information */
 	/*@{ */
-	spinlock_t object_name_lock;
+	struct mutex object_name_lock;
 	struct idr object_name_idr;
 	/*@} */
 	int switch_power_state;