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/common/env_sf.c b/common/env_sf.c
index 9944602..45f441a 100644
--- a/common/env_sf.c
+++ b/common/env_sf.c
@@ -10,6 +10,7 @@
  * SPDX-License-Identifier:	GPL-2.0+
  */
 #include <common.h>
+#include <dm.h>
 #include <environment.h>
 #include <malloc.h>
 #include <spi.h>