x86: ifdtool: Allow creation of an empty ROM

Allow an empty ROM to be created, without needing to provide a descriptor.
The descriptor is not needed on some x86 boards.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/ifdtool.c

@@ -924,7 +924,7 @@ int main(int argc, char *argv[])
 
 	if ((mode_dump + mode_extract + mode_inject + mode_spifreq +
 	     mode_em100 + mode_locked + mode_unlocked + mode_write +
-	     mode_write_descriptor) == 0) {
+	     mode_write_descriptor) == 0 && !create) {
 		fprintf(stderr, "You need to specify a mode.\n\n");
 		print_usage(argv[0]);
 		exit(EXIT_FAILURE);