mtd: spi-mem: 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/spi/spi-mem.c b/drivers/spi/spi-mem.c
index d344701..c095ae9 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -13,9 +13,14 @@
 #include <linux/pm_runtime.h>
 #include "internals.h"
 #else
-#include <dm/device_compat.h>
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <malloc.h>
+#include <spi.h>
 #include <spi.h>
 #include <spi-mem.h>
+#include <dm/device_compat.h>
 #endif
 
 #ifndef __UBOOT__