kernel - Tag vm_map_entry structure, slight optimization to zalloc, misc.

kernel - Tag vm_map_entry structure, slight optimization to zalloc, misc.

* Tag the vm_map_entry structure, allowing debugging programs to
  break-down how KMEM is being used more easily.

  This requires an additional argument to vm_map_find() and most
  kmem_alloc*() functions.

* Remove the page chunking parameter to zinit() and zinitna().  It was
  only being used degeneratively.  Increase the chunking from one page
  to four pages, which will reduce the amount of vm_map_entry spam in
  the kernel_map.

* Use atomic ops when adjusting zone_kern_pages.