kernel - Remove SMP bottlenecks on uidinfo, descriptors, and lockf

kernel - Remove SMP bottlenecks on uidinfo, descriptors, and lockf

* Use an eventcounter and the per-thread fd cache to fix
  bottlenecks in checkfdclosed().  This will work well for
  the vast majority of applications and test benches.

* Batch holdfp*() operations on kqueue collections when implementing
  poll() and select().  This significant improves performance.
  Full scaling not yet achieved, however.

* Increase copyin item batching from 8 to 32 for select() and poll().

* Give the uidinfo structure a pcpu array to hold the posixlocks
  and openfiles count fields, with a rollup contained in the uidinfo
  structure itself.

  This removes numerous global bottlenecks related to open(),
  close(), dup*(), and lockf operations (posixlocks count).

  ui_openfiles will force a rollup on limit reached to be sure
  that the limit was actually reached.  ui_posixlocks stays fairly
  loose.  Each cpu rolls up generally only when the pcpu count exceeds
  +32 or goes below -32.

* Give the proc structure a pcpu array for the same counts, in order
  to properly support seteuid() and such.

* Replace P_ADVLOCK with a char field proc->p_advlock_flag, and
  remove token operations around the field.