dm: Support driver model prior to relocation

Initialise devices marked 'pre-reloc' and make them available prior to
relocation. Note that this requires pre-reloc malloc() to be available.

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

include/asm-generic/global_data.h

@@ -65,7 +65,8 @@ typedef struct global_data {
 	struct global_data *new_gd;	/* relocated global data */
 
 #ifdef CONFIG_DM
-	struct udevice	*dm_root;/* Root instance for Driver Model */
+	struct udevice	*dm_root;	/* Root instance for Driver Model */
+	struct udevice	*dm_root_f;	/* Pre-relocation root instance */
 	struct list_head uclass_root;	/* Head of core tree */
 #endif