When a copy-on-write fault occurs, pmap_enter() is called on to replace the
mapping to the old read-only page with a mapping to the new read-write page.
To destroy the old mapping, pmap_enter() must destroy its page table and PV
entries and invalidate its TLB entry. This change simply invalidates that
TLB entry a little earlier, specifically, on amd64 and arm64, before the PV
list lock is held.

Reviewed by: kib, markj
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D23027