x86/svm: add support for pause filtering threshold

x86/svm: add support for pause filtering threshold

Add support for enabling the pause filtering threshold feature.  This
causes the pause filtering count to reset if there's pause filtering
threshold cycles or greater between pauses.  See AMD APM Vol 2 Section
15.14.4 for more details.

The values of the pause filtering count and threshold were found by
iterating over different values of the count and threshold while running
kernbench and a pi spigot algorithm with yields placed in it.  A
balanced setting for both variable provides:

(Using averaged elapsed time with kernbench)
old = 852.0
new = 848.8
improvement = .4%

For system without pause filtering threshold, the change, from 3000 to
4000 for the count, should not negatively effect system performance.

Signed-off-by: Brian Woods <brian.woods@amd.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>