drm: Define drm_mm_for_each_node_in_range()

Some clients would like to iterate over every node within a certain
range. Make a nice little macro for them to hide the mixing of the
rbtree search and linear walk.

v2: Blurb

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161123141118.23876-1-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index 632473b..f8eebbd 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -174,19 +174,12 @@ INTERVAL_TREE_DEFINE(struct drm_mm_node, rb,
 		     START, LAST, static inline, drm_mm_interval_tree)
 
 struct drm_mm_node *
-drm_mm_interval_first(struct drm_mm *mm, u64 start, u64 last)
+__drm_mm_interval_first(struct drm_mm *mm, u64 start, u64 last)
 {
 	return drm_mm_interval_tree_iter_first(&mm->interval_tree,
 					       start, last);
 }
-EXPORT_SYMBOL(drm_mm_interval_first);
-
-struct drm_mm_node *
-drm_mm_interval_next(struct drm_mm_node *node, u64 start, u64 last)
-{
-	return drm_mm_interval_tree_iter_next(node, start, last);
-}
-EXPORT_SYMBOL(drm_mm_interval_next);
+EXPORT_SYMBOL(__drm_mm_interval_first);
 
 static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
 					  struct drm_mm_node *node)