drivers: watchdog: add andes atcwdt200 support

This patch adds an implementation of the Andes watchdog ATCWDT200 driver.

Signed-off-by: CL Wang <cl634@andestech.com>
Signed-off-by: Randolph <randolph@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>