watchdog: twl4030_wdt: add DT support

Add DT support for twl4030_wdt. This is needed to get twl4030_wdt to
probe when booting with DT.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>