Revert "arm: Remove nsa310s board"

While this platform has not yet been converted, there is active efforts
to do so.  Keep the platform for now.

This reverts commit aa697e6904ba1b3144a46ec642d4695e7c0cdc3e.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/zyxel/nsa310s/Makefile b/board/zyxel/nsa310s/Makefile
new file mode 100644
index 0000000..2131e28
--- /dev/null
+++ b/board/zyxel/nsa310s/Makefile
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Copyright (C) 2015
+# Gerald Kerma <dreagle@doukki.net>
+# Tony Dinh <mibodhi@gmail.com>
+
+obj-y	:= nsa310s.o