mkimage: fit: Fix signing of configs with external data

Just like we exclude data-size, data-position, and data-offset from
fit_config_check_sig, we must exclude them while signing as well.

While we're at it, use the FIT_DATA_* defines for fit_config_check_sig
as welll.

Fixes: 8edecd3110e ("fit: Fix verification of images with external data")
Fixes: c522949a29d ("rsa: sig: fix config signature check for fit with padding")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/image-fit-sig.c b/boot/image-fit-sig.c
index a461d59..1236989 100644
--- a/boot/image-fit-sig.c
+++ b/boot/image-fit-sig.c
@@ -260,10 +260,10 @@
 				char **err_msgp)
 {
 	static char * const exc_prop[] = {
-		"data",
-		"data-size",
-		"data-position",
-		"data-offset"
+		FIT_DATA_PROP,
+		FIT_DATA_SIZE_PROP,
+		FIT_DATA_POSITION_PROP,
+		FIT_DATA_OFFSET_PROP,
 	};
 
 	const char *prop, *end, *name;