MFC: r216891

MFC: r216891

Extend the section in which interrupts are disabled in the TLB demap
functions, otherwise if we get preempted after checking whether a certain
pmap is active on the current CPU but before disabling interrupts we might
operate on an outdated state as the pmap might have been deactivated in
the meantime. As the same issue may arises when the TLB demap function is
interrupted by a TLB demap IPI, just entering a critical section before
the check isn't sufficient so we have to fully disable interrupts instead.

git-svn-id: svn://svn.freebsd.org/base/stable/8@216989 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f