perf list: Add s390 support for detailed PMU event description

perf list: Add s390 support for detailed PMU event description

Correct the support of detailed/verbose PMU event description by using
the "Unit": keyword in the json files to address event names refering to
the /sys/devices/cpum_[cs]f devices.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Link: http://lkml.kernel.org/r/20180621080452.61012-2-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>