dm: core: Provide a way to reset the device tree

At present there is only one device tree used by the ofnode functions,
except for some esoteric use of live tree. In preparation for supporting
more than one, add a way to reset the list of device trees.

For now this does nothing.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/board_r.c

@@ -234,6 +234,8 @@ static int initr_dm(void)
 {
 	int ret;
 
+	oftree_reset();
+
 	/* Save the pre-reloc driver model and start a new one */
 	gd->dm_root_f = gd->dm_root;
 	gd->dm_root = NULL;