Allow ppc64 events to be specified with or without _GRP<n> suffix
All events for IBM PowerPC server processors (except CYCLES) have
a _GRP<n> suffix. This is because the legacy opcontrol profiler
can only profile events in the same group (i.e., having the same
_GRP<n> suffix). But operf has no such restriction because it
can multiplex events; thus, so we should allow the user to pass
event names without the _GRP<n> suffix.
Signed-off-by: Maynard Johnson <email@example.com>