dm: Use dm.h header when driver mode is used

This header includes things that are needed to make driver build. Adjust
existing users to include that always, even if other dm/ includes are
present

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/armltd/vexpress64/vexpress64.c b/board/armltd/vexpress64/vexpress64.c
index 0a22417..26e22c4 100644
--- a/board/armltd/vexpress64/vexpress64.c
+++ b/board/armltd/vexpress64/vexpress64.c
@@ -6,12 +6,12 @@
  * SPDX-License-Identifier:	GPL-2.0+
  */
 #include <common.h>
+#include <dm.h>
 #include <malloc.h>
 #include <errno.h>
 #include <netdev.h>
 #include <asm/io.h>
 #include <linux/compiler.h>
-#include <dm/platdata.h>
 #include <dm/platform_data/serial_pl01x.h>
 #include "pcie.h"
 #include <asm/armv8/mmu.h>