image: Rename fit_add_hashes() to fit_add_verification_data()

We intend to add signatures to FITs also, so rename this function so that
it is not specific to hashing. Also rename fit_image_set_hashes() and
make it static since it is not used outside this file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>
diff --git a/tools/fit_image.c b/tools/fit_image.c
index 76bbba1..8f51159 100644
--- a/tools/fit_image.c
+++ b/tools/fit_image.c
@@ -125,7 +125,7 @@
 	}
 
 	/* set hashes for images in the blob */
-	if (fit_set_hashes (ptr)) {
+	if (fit_add_verification_data(ptr)) {
 		fprintf (stderr, "%s Can't add hashes to FIT blob",
 				params->cmdname);
 		unlink (tmpfile);