MIPS: Loongson1: Add watchdog support for Loongson1 board

The patch adds watchdog support for Loongson1 board.

Signed-off-by: Yang Ling <gnaygnil@gmail.com>
Cc: keguang.zhang@gmail.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/14644/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>