watchdog: coh901327: devicetree support

This adds support for probing the COH 901 327 watchdog from
the device tree and also adds associated bindings.

Acked-by: Wim Van Sebroeck <wim@iguana.be>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>