Add support for multi-watchdog systems

[troglobit]

The native finit-watchdogd and finit itself can only handle one system watchdog at the moment. However, many SoCs now have support for multiple WDTs, usually one per CPU core. In watchdogd, support for multi-watchdog systems will soon be added, so it will need to be able to hand-over particular devnodes, this will be sent in the data[] part of the hand-over request.