cbfstool: expose cbfs_calculate_file_header_size()

Headers vary in size soon, and more places need to be able to calculate their
size.

Change-Id: I30761bb9da0756418993dee21d8fa18cf3174c40
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/11214
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/util/cbfstool/cbfs_image.c b/util/cbfstool/cbfs_image.c
index e78ee40..ed065b0 100644
--- a/util/cbfstool/cbfs_image.c
+++ b/util/cbfstool/cbfs_image.c
@@ -112,7 +112,7 @@
 
 /* CBFS image */
 
-static size_t cbfs_calculate_file_header_size(const char *name)
+size_t cbfs_calculate_file_header_size(const char *name)
 {
 	return (sizeof(struct cbfs_file) +
 		align_up(strlen(name) + 1, CBFS_FILENAME_ALIGN));