nand: Drop dm.h header file

This header file should not be included in other header files. Remove it
and use a forward declaration instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/mtd/nand/raw/brcmnand/brcmnand_compat.c b/drivers/mtd/nand/raw/brcmnand/brcmnand_compat.c
index c586798..a6acf55 100644
--- a/drivers/mtd/nand/raw/brcmnand/brcmnand_compat.c
+++ b/drivers/mtd/nand/raw/brcmnand/brcmnand_compat.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+
 
 #include <common.h>
+#include <dm.h>
 #include <malloc.h>
 #include <dm/devres.h>
 #include "brcmnand_compat.h"