watchdog: bindings: dw_wdt: add reset lines

Document the reset lines holding the watchdog core in reset.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-watchdog@vger.kernel.org
Cc: devicetree@vger.kernel.org
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>