System reset callout

The miscellaneous callout, reboot(), gets called whenever the kernel needs to reboot the machine.

The reboot() callout is responsible for resetting the system. This callout lets developers customize the events that occur when proc needs to reboot — such as turning off a watchdog, banging the right registers etc. without customizing proc each time.

A "shutdown" of the binary will call sysmgr_reboot(), which will eventually trigger the reboot() callout.