MFC 245577,245640:

MFC 245577,245640:
Don't attempt to use clflush on the local APIC register window.  Various
CPUs exhibit bad behavior if this is done (Intel Errata AAJ3, hangs on
Pentium-M, and trashing of the local APIC registers on a VIA C7).  The
local APIC is implicitly mapped UC already via MTRRs, so the clflush isn't
necessary anyway.

git-svn-id: svn://svn.freebsd.org/base/stable/8@247548 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f