kernel - Move CPUMASK_LOCK out of the cpumask_t

kernel - Move CPUMASK_LOCK out of the cpumask_t

* Add cpulock_t (a 32-bit integer on all platforms) and implement
  CPULOCK_EXCL as well as space for a counter.

* Break-out CPUMASK_LOCK, add a new field to the pmap (pm_active_lock)
  and do the process vmm (p_vmm_cpulock) and implement the mmu interlock
  there.

  The VMM subsystem uses additional bits in cpulock_t as a mask counter
  for implementing its interlock.

  The PMAP subsystem just uses the CPULOCK_EXCL bit in pm_active_lock for
  its own interlock.

* Max cpus on 64-bit systems is now 64 instead of 63.

* cpumask_t is now just a pure cpu mask and no longer requires all-or-none
  atomic ops, just normal bit-for-bit atomic ops.  This will allow us to
  hopefully extend it past the 64-cpu limit soon.