perf vendor events s390: Use s390 machine name instead of type 8561

In the pmu-events directory for JSON file definitions use the
official machine name IBM z15 instead of machine type number
8561. This is consistent with previous machines.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Link: http://lore.kernel.org/lkml/20190927081147.18345-2-tmricht@linux.ibm.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>