drm: move ttm global code to core drm

I wrote this for the prime sharing work, but I also noticed other external
non-upstream drivers from a large company carrying a similiar patch, so I
may as well ship it in master.

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 9763288..cb4cf7e 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -1395,7 +1395,7 @@
 	kfree(glob);
 }
 
-void ttm_bo_global_release(struct ttm_global_reference *ref)
+void ttm_bo_global_release(struct drm_global_reference *ref)
 {
 	struct ttm_bo_global *glob = ref->object;
 
@@ -1404,7 +1404,7 @@
 }
 EXPORT_SYMBOL(ttm_bo_global_release);
 
-int ttm_bo_global_init(struct ttm_global_reference *ref)
+int ttm_bo_global_init(struct drm_global_reference *ref)
 {
 	struct ttm_bo_global_ref *bo_ref =
 		container_of(ref, struct ttm_bo_global_ref, ref);