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/drivers/ram/bmips_ram.c b/drivers/ram/bmips_ram.c
index ac35fbe..7efcc8f 100644
--- a/drivers/ram/bmips_ram.c
+++ b/drivers/ram/bmips_ram.c
@@ -9,10 +9,10 @@
  */
 
 #include <common.h>
+#include <dm.h>
 #include <errno.h>
 #include <ram.h>
 #include <asm/io.h>
-#include <dm/device.h>
 
 #define SDRAM_CFG_REG		0x0
 #define SDRAM_CFG_COL_SHIFT	4