watchdog: move WATCHDOG_TIMEOUT_MSECS to Kconfig

move WATCHDOG_TIMEOUT_MSECS to Kconfig and fix
all board defconfigs.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>
Acked-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Martyn Welch <martyn.welch@collabora.com>
Signed-off-by: Stefan Roese <sr@denx.de>