MFC r349003, r349031, r349042, r349129, r349290, r349618, r349798

MFC r349003, r349031, r349042, r349129, r349290, r349618, r349798
  Change pmap_demote_l2_locked() so that it removes the superpage mapping on
  a demotion failure.  Otherwise, some callers to pmap_demote_l2_locked(),
  such as pmap_protect(), may leave an incorrect mapping in place on a
  demotion failure.

  Change pmap_demote_l2_locked() so that it handles addresses that are not
  superpage aligned.  Some callers to pmap_demote_l2_locked(), such as
  pmap_protect(), may not pass a superpage aligned address.

  Optimize TLB invalidation in pmap_remove_l2().

  Change the arm64 pmap so that updates to the global count of wired pages
  are not performed directly by the pmap.  Instead, they are performed by
  vm_page_free_pages_toq().

  Batch the TLB invalidations that are performed by pmap_protect() rather
  than performing them one at a time.

  Eliminate a redundant call to pmap_invalidate_page() from
  pmap_ts_referenced().

  Introduce pmap_remove_l3_range() and use it in two places: (1)
  pmap_remove(), where it eliminates redundant TLB invalidations by
  pmap_remove() and pmap_remove_l3(), and (2) pmap_enter_l2(), where it may
  optimize the TLB invalidations by batching them.

  Implement pmap_copy().

  Three changes to pmap_enter():

  1. Use _pmap_alloc_l3() instead of pmap_alloc_l3() in order to handle the
  possibility that a superpage mapping for "va" was created while we slept.

  2. Eliminate code for allocating kernel page table pages.  Kernel page
  table pages are preallocated by pmap_growkernel().

  3. Eliminate duplicated unlock operations when KERN_RESOURCE_SHORTAGE is
  returned.