kernel - Add vmobj_token, misc vm-related tokenization

kernel - Add vmobj_token, misc vm-related tokenization

* Add vmobj_token to protect vm_object_list and vm_object->ref_count and
  related functions.

  Note: coalesce and collapse require both vm_token and vmobj_token,
  and vmspace_fork() requires a bunch of tokens.

* Remove miscellanious mplocks and critical sections that are no longer
  needed.

* Correct potential sysinfo kernel data visibilty issue.

* Optimize some potentially recursive vm_token/vmobj_token situations
  by adding *_locked() procedure variants.  To avoid blowing out the
  token stack.

* Remove unnecessary get_mplock() calls in vm_zone.c

* Bump gd_intr_nesting_level in the IPI processing core and assert
  that it is zero in the gettoken core.  Hard interrupts (vs interrupt
  threads) are not allowed to acquire tokens for obvious reasons.