perf test: Add git ignore for perf data generated by the ARM CoreSight tests

Ignore perf output data files generated by perf tests for cleaner git
status.

Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Carsten Haitzler <carsten.haitzler@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight@lists.linaro.org
Link: https://lore.kernel.org/r/20220909152803.2317006-6-carsten.haitzler@foss.arm.com


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