perf list: Add PMU pai_ext event description for IBM z16

Add the event description for the IBM z16 pai_ext PMU released with
commit c432fefe

 ("s390/pai: Add support for PAI Extension 1 NNPA
counters")

The document SA22-7832-13 "z/Architecture Principles of Operation",
published May, 2022, contains the description of the
Processor Activity Instrumentation Facility and the NNPA counter
set., See Pages 5-113 to 5-116 and chapter 26 for details.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: https://lore.kernel.org/r/20230308125326.2195613-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>