fit: add sha256 support

add sha256 support to fit images

Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/sha256.c b/tools/sha256.c
new file mode 100644
index 0000000..8ca931f
--- /dev/null
+++ b/tools/sha256.c
@@ -0,0 +1 @@
+#include "../lib/sha256.c"