procd: add start-console support

procd: add start-console support

This adds a hotplug function to (re-)start inittab entries with askfirst or respawn.

At the moment the devices used with these actions must be present during boot
otherwise such lines are skipped.

However, this prevents having inittab entries with consoles for e.g. USB gadget
devices which only appear after kernel module loading and after configuring them
with configfs.

While it was possible to only scan the inittab for the desired item to start,
I assume the inittab to be short and re-running the whole list will be negligible.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>