iommu/vt-d: Add PRQ handling latency sampling

The execution time for page fault request handling is performance critical
and needs to be monitored. This adds code to sample the execution time of
page fault request handling.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20210520031531.712333-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20210610020115.1637656-17-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>