sparc64: perf: Fix the mapping between perf events and perf counters

sparc64: perf: Fix the mapping between perf events and perf counters

Up until now, perf event[0] has been counted on perf counter[0],
perf event[1] on perf counter[1] etc. However, there is no reason why
this has to be the case. Infact, on SPARC-M8 some events can only be
counted on a sub set of the available perf counters, rather than all
the available perf counters. Whilst adding these perf counter
constraints for the SPARC-M8 it became apparent that some confusion
had crept into the existing code.

Some functions were making the assumption that the perf event index was
equivalent to the perf counter index. This commit fixes these assumptions,
and allows for the case where perf event[0] is not counted on
perf counter[0] etc.

Orabug: 23333572

Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com>
Reviewed-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>