mount_root: add support for passing args to mount_root start

It may be useful to pass args to mount_root start call. One usecase
might be pass additional configuration to enable special option on
mounting rootfs. Change main logic and permit additional args when start
is used.

No functional change intended as the default behaviour is saved by
continuing to call start if no args are provided.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>

mount_root.c

@@ -119,7 +119,7 @@ done(int argc, char *argv[1])
 
 int main(int argc, char **argv)
 {
-	if (argc < 2)
+	if (argc < 2) || (!strcmp(argv[1], "start"))
 		return start(argc, argv);
 	if (!strcmp(argv[1], "ram"))
 		return ramoverlay();