tools, fit_check_sign: verify a signed fit image

add host tool "fit_check_sign" which verifies, if a fit image is
signed correct.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
diff --git a/tools/rsa-checksum.c b/tools/rsa-checksum.c
new file mode 100644
index 0000000..09033e6
--- /dev/null
+++ b/tools/rsa-checksum.c
@@ -0,0 +1 @@
+#include "../lib/rsa/rsa-checksum.c"