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/cadence/xtfpga/xtfpga.c b/board/cadence/xtfpga/xtfpga.c
index 39b9b12..0265e9b 100644
--- a/board/cadence/xtfpga/xtfpga.c
+++ b/board/cadence/xtfpga/xtfpga.c
@@ -7,7 +7,7 @@
 
 #include <common.h>
 #include <command.h>
-#include <dm/platdata.h>
+#include <dm.h>
 #include <dm/platform_data/net_ethoc.h>
 #include <linux/ctype.h>
 #include <linux/string.h>