s390/pai_ext: Enable per-task and system-wide sampling event

The PMU for PAI NNPA counters enforces the following restriction:

 - No per-task context for PAI sampling event NNPA_ALL
 - No multiple system-wide PAI sampling event NNPA_ALL

Both restrictions are removed. One or more per-task sampling events
are supported. Also one or more system-wide sampling events are
supported.

Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>