MFC r232917:

MFC r232917:
Rewrite thread CPU usage percentage math to not depend on periodic calls
with HZ rate through the sched_tick() calls from hardclock().

Potentially it can be used to improve precision, but now it is just minus
one more reason to call hardclock() for every HZ tick on every active CPU.
SCHED_4BSD never used sched_tick(), but keep it in place for now, as at
least SCHED_FBFS existing in patches out of the tree depends on it.

git-svn-id: svn://svn.freebsd.org/base/stable/9@234166 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f