MFC r209789

MFC r209789
  Correctly maintain the per-cpu field "curpmap" on amd64 just like we
  do on i386.  The consequences of not doing so on amd64 became apparent
  with the introduction of the COUNT_IPIS and COUNT_XINVLTLB_HITS
  options.  Specifically, single-threaded applications were generating
  unnecessary IPIs to shoot-down the TLB on other processors.

MFC r209887
  Reduce the number of global TLB shootdowns generated by pmap_qenter().
  Specifically, teach pmap_qenter() to recognize the case when it is being
  asked to replace a mapping with the very same mapping and not generate
  a shootdown.

git-svn-id: svn://svn.freebsd.org/base/stable/8@213887 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f