watchdog: loongson1_wdt: Implement restart handler

Implement restart handler for the Loongson-1 watchdog driver and
define the watchdog registers instead of including the legacy header.

Signed-off-by: Keguang Zhang <keguang.zhang@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20230330112051.551648-3-keguang.zhang@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>