s390/pai_ext: Enable concurrent system-wide counting/sampling

s390/pai_ext: Enable concurrent system-wide counting/sampling

The PMU for PAI NNPA counters enforces the following restriction:

- No system wide counting while system wide sampling is active.

This restriction is removed. One or more system wide counting events
can now be active at the same time while at most one system wide
sampling event is active.

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>