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/root.c b/drivers/core/root.c
index 2a5ebec..3adbc94 100644
--- a/drivers/core/root.c
+++ b/drivers/core/root.c
@@ -45,8 +45,8 @@
 {
 	/* The sentinel node has moved, so update things that point to it */
 	if (gd->dm_root) {
-		new_gd->uclass_root.next->prev = &new_gd->uclass_root;
-		new_gd->uclass_root.prev->next = &new_gd->uclass_root;
+		new_gd->uclass_root->next->prev = new_gd->uclass_root;
+		new_gd->uclass_root->prev->next = new_gd->uclass_root;
 	}
 }
 
@@ -136,7 +136,8 @@
 		dm_warn("Virtual root driver already exists!\n");
 		return -EINVAL;
 	}
-	INIT_LIST_HEAD(&DM_UCLASS_ROOT_NON_CONST);
+	gd->uclass_root = &DM_UCLASS_ROOT_S_NON_CONST;
+	INIT_LIST_HEAD(DM_UCLASS_ROOT_NON_CONST);
 
 	if (IS_ENABLED(CONFIG_NEEDS_MANUAL_RELOC)) {
 		fix_drivers();