MFC r315361 and r315364: Hide MONITORX/MWAITX from guests.

MFC  r315361 and  r315364: Hide MONITORX/MWAITX from guests.

r315361
  Add the AMD MONITORX/MWAITX feature definition introduced in
  Bulldozer/Ryzen CPUs.

r315364
  Hide the AMD MONITORX/MWAITX capability.
  Otherwise, recent Linux guests will use these instructions, resulting
  in #UD exceptions since bhyve doesn't implement MONITOR/MWAIT exits.

  This fixes boot-time hangs in recent Linux guests on Ryzen CPUs
  (and probably Bulldozer aka AMD FX as well).

git-svn-id: svn://svn.freebsd.org/base/stable/10@315928 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f