x86/AMD: Stop counters on VPMU save

x86/AMD: Stop counters on VPMU save

Stop the counters during VPMU save operation since they shouldn't be
running when VPCU that controls them is not. This also makes it
unnecessary to check for overflow in context_restore()

Set LVTPC vector before loading the context during vpmu_restore().
Otherwise it is possible to trigger an interrupt without proper vector.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>