coresight: pmu: Adds return stack option to perf coresight pmu

Return stack is a programmable option on some ETM and PTM hardware.
Adds the option flags to enable this from the perf event command line.

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
index 7d41026..45852c2 100644
--- a/include/linux/coresight-pmu.h
+++ b/include/linux/coresight-pmu.h
@@ -24,6 +24,7 @@
 /* ETMv3.5/PTM's ETMCR config bit */
 #define ETM_OPT_CYCACC  12
 #define ETM_OPT_TS      28
+#define ETM_OPT_RETSTK	29
 
 static inline int coresight_get_trace_id(int cpu)
 {