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/doc/uImage.FIT/signature.txt b/doc/uImage.FIT/signature.txt
index 71f8b6c..9502037 100644
--- a/doc/uImage.FIT/signature.txt
+++ b/doc/uImage.FIT/signature.txt
@@ -357,6 +357,9 @@
 Test Verified Boot Run: unsigned config: OK
 Sign images
 Test Verified Boot Run: signed config: OK
+check signed config on the host
+OK
+Test Verified Boot Run: signed config: OK
 Test Verified Boot Run: signed config with bad hash: OK
 do sha256 test
 Build FIT with signed images
@@ -367,6 +370,9 @@
 Test Verified Boot Run: unsigned config: OK
 Sign images
 Test Verified Boot Run: signed config: OK
+check signed config on the host
+OK
+Test Verified Boot Run: signed config: OK
 Test Verified Boot Run: signed config with bad hash: OK
 
 Test passed