Add an xdr function for the cbfs_file header

And use it in fit.c and remove one more use of htonl.

Change-Id: Ibf18dcc0a7f08d75c2374115de0db7a4bf64ec1e
Signed-off-by: Ronald G. Minnich <rminnich@google.com>
Reviewed-on: http://review.coreboot.org/5120
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

util/cbfstool/common.h

@@ -110,5 +110,6 @@ struct xdr {
 
 /* xdr.c */
 extern struct xdr xdr_le, xdr_be;
+int bgets(struct buffer *input, void *output, size_t len);
 
 #endif