om-watchdog: add support for Teltonika RUT5xx (ramips)

Add rut5xx GPIO PIN selection to om-package startup script.

Testet on a RUT500 device, the timeout value of the hardware watchdog
is about 280 sec.

Signed-off-by: Steffen Weinreich <steve@weinreich.org>
[split into two commits, bump PKG_RELEASE]
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>