sched_schedcpu() is called only during SYSINIT to start kthread that
calls schedcpu() every second in 4BSD, but its name implies it's doing
what 4BSD's schedcpu() does. Rename this function to sched_sysinit() to
mark that schedulers can use it for its own SYSINIT routine. Note that
their SYSINIT routine does not necessarily need to be similar to 4BSD's
decay in schedcpu().
The scheduler.9 man page is planned to be rewritten from scratch, so no
change to it for now.
MFC after: 2 weeks
MFC to: stable/14, stable/15
Sponsored by: FreeBSD Foundation, Reliable Computer Systems Lab