watchdog: jz4740: Add DT support

Add DT support to the jz4740 driver. Simple of_match_ptr. No other
modification for probe needed

Signed-off-by: Zubair Lutfullah Kakakhel <Zubair.Kakakhel@imgtec.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>