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/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
index 4dbe6a5..eb24222 100644
--- a/arch/arm/lib/bootm.c
+++ b/arch/arm/lib/bootm.c
@@ -14,7 +14,7 @@
 
 #include <common.h>
 #include <command.h>
-#include <dm/device.h>
+#include <dm.h>
 #include <dm/root.h>
 #include <image.h>
 #include <u-boot/zlib.h>