watchdog: Add interface to config timeout and pretimeout in sysfs

ascend inclusion
category: feature
bugzilla: NA
CVE: NA

Those interfaces exist already in sysfs of watchdog driver core, but
they are readonly. This patch add write hook so we can config timeout
and pretimeout by writing those files.

Use Kconfig ASCEND_WATCHDOG_SYSFS_CONFIGURE to select this feature.

Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>