vmx: Add support for Pause-Loop Exiting

New NHM processors will support Pause-Loop Exiting by adding 2
VM-execution control fields:
PLE_Gap    - upper bound on the amount of time between two successive
             executions of PAUSE in a loop.
PLE_Window - upper bound on the amount of time a guest is allowed to
             execute in a PAUSE loop

If the time, between this execution of PAUSE and previous one, exceeds
the PLE_Gap, processor consider this PAUSE belongs to a new loop.
Otherwise, processor determins the the total execution time of this
loop(since 1st PAUSE in this loop), and triggers a VM exit if total
time exceeds the PLE_Window.
* Refer SDM volume 3b section 21.6.13 & 22.1.3.

Pause-Loop Exiting can be used to detect Lock-Holder Preemption, where
one VP is sched-out after hold a spinlock, then other VPs for same
lock are sched-in to waste the CPU time.

Our tests indicate that most spinlocks are held for less than 2^12
cycles.  Performance tests show that with 2X LP over-commitment we can
get +2% perf improvement for kernel build(Even more perf gain with
more LPs).

Signed-off-by: Zhai Edwin <edwin.zhai@intel.com>

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