drm/ttm: make global mutex and use count static

Only needed during device hot plug and remove and not exported.
Signed-off-by: Christian König <christian.koenig@amd.com>
Suggested-by: Bernard <bernard@vivo.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210409110730.2958-1-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_device.c

@@ -39,8 +39,8 @@
 /**
  * ttm_global_mutex - protecting the global state
  */
-DEFINE_MUTEX(ttm_global_mutex);
-unsigned ttm_glob_use_count;
+static DEFINE_MUTEX(ttm_global_mutex);
+static unsigned ttm_glob_use_count;
 struct ttm_global ttm_glob;
 EXPORT_SYMBOL(ttm_glob);