Consolidate devstat piece and share I/O related pages, -vm, -zarc, and -swap pages.
Ref - https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=213310
Removed some of experimental code.
A couple of month delay is a minor.
I just started thinking to add few more enhancements.
It will be nice if you pick up next one, too ( coming in a couple of months, too).