mkimage: fit_image: Add support for SOURCE_DATE_EPOCH in signatures

When generating timestamps in signatures, use imagetool_get_source_date()
so we can be overridden by SOURCE_DATE_EPOCH to generate reproducible
images.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Simon Glass <sjg@chromum.org>
diff --git a/tools/fit_image.c b/tools/fit_image.c
index 6f09a66..3c26535 100644
--- a/tools/fit_image.c
+++ b/tools/fit_image.c
@@ -60,7 +60,8 @@
 		ret = fit_add_verification_data(params->keydir, dest_blob, ptr,
 						params->comment,
 						params->require_keys,
-						params->engine_id);
+						params->engine_id,
+						params->cmdname);
 	}
 
 	if (dest_blob) {