dm: Add spi.h header to a few files

Some files are using SPI functions but not explitly including the SPI
header file. Fix this, since driver model needs it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
diff --git a/drivers/dfu/dfu_sf.c b/drivers/dfu/dfu_sf.c
index 91f6df2..c3d3c3b 100644
--- a/drivers/dfu/dfu_sf.c
+++ b/drivers/dfu/dfu_sf.c
@@ -9,6 +9,7 @@
 #include <errno.h>
 #include <div64.h>
 #include <dfu.h>
+#include <spi.h>
 #include <spi_flash.h>
 
 static long dfu_get_medium_size_sf(struct dfu_entity *dfu)