kernel - Optimize spinlocks for 48-core contention

kernel - Optimize spinlocks for 48-core contention

* Change the spinlock algorithm to do a read-test before atomic_swap_int().
  This has no effect on single-chip cpus (tested on phenom II quad-core),
  but has a HUGE HUGE HUGE effect on multi-chip/many-core systems.  On
  monster (48-core opteron / 4 x 12-core chips) concurrent kernel compile
  time is reduced from 170 seconds to 75 seconds with this one change.
  That's well over 100%.

  The reason the change is important is because it unloads the hardware
  cache coherency bus and communication by creating a closed-loop with
  the pre-read, which essentially passively waits for the cache update
  instead of actively issuing a locked bus cycle memory op.  This prevents
  total armagheddon on the memory busses when a substantial number of
  cores are doing real work.

* Increase the number of pool spinlocks from 1024 to 8192.  We need them
  now that vm_page's use pool spinlocks.