dt-bindings: watchdog: loongson,ls1x-wdt: Add ls2k0300-wdt compatible

dt-bindings: watchdog: loongson,ls1x-wdt: Add ls2k0300-wdt compatible

Add "loongson,ls2k0300-wdt" compatible to the dt-schema document, which
is similar to Loongson-1 watchdog, but with differences in some register
offsets and bit definitions.

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
pw-bot: not-applicable
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>