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/common/env_sf.c b/common/env_sf.c
index 37ab13a..5e3729c 100644
--- a/common/env_sf.c
+++ b/common/env_sf.c
@@ -12,6 +12,7 @@
 #include <common.h>
 #include <environment.h>
 #include <malloc.h>
+#include <spi.h>
 #include <spi_flash.h>
 #include <search.h>
 #include <errno.h>