perf cs-etm: Add helper cs_etm__get_pid_fmt()

perf cs-etm: Add helper cs_etm__get_pid_fmt()

This patch adds helper function cs_etm__get_pid_fmt(), by passing
parameter "traceID", it returns the PID format.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Link: https://lore.kernel.org/r/20210213113220.292229-5-leo.yan@linaro.org
Link: https://lore.kernel.org/r/20210224164835.3497311-6-mathieu.poirier@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>