mm: write-lock VMAs before removing them from VMA tree

Write-locking VMAs before isolating them ensures that page fault handlers
don't operate on isolated VMAs.

[surenb@google.com: mm/nommu: remove unnecessary VMA locking]
  Link: https://lkml.kernel.org/r/20230301190457.1498985-1-surenb@google.com
  Link: https://lore.kernel.org/all/Y%2F8CJQGNuMUTdLwP@localhost/
Link: https://lkml.kernel.org/r/20230227173632.3292573-19-surenb@google.com


Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>