dm: core: Allow the uclass list to move

At present the uclass list head is in global_data. This is convenient
but with the new of-platdata we need the list head to be declared by
the generated code.

Change this over to be a pointer. Provide a 'static' version in
global_data to retain the current behaviour.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index e773e34..cdb975d 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -33,7 +33,7 @@
 	 * node to the start of the list, or creating a linear array mapping
 	 * id to node.
 	 */
-	list_for_each_entry(uc, &gd->uclass_root, sibling_node) {
+	list_for_each_entry(uc, gd->uclass_root, sibling_node) {
 		if (uc->uc_drv->id == key)
 			return uc;
 	}
@@ -84,7 +84,7 @@
 	uc->uc_drv = uc_drv;
 	INIT_LIST_HEAD(&uc->sibling_node);
 	INIT_LIST_HEAD(&uc->dev_head);
-	list_add(&uc->sibling_node, &DM_UCLASS_ROOT_NON_CONST);
+	list_add(&uc->sibling_node, DM_UCLASS_ROOT_NON_CONST);
 
 	if (uc_drv->init) {
 		ret = uc_drv->init(uc);