perf: add PMU_EVENT_ATTR_STRING() helper

Helper for constructing static struct perf_pmu_events_attr s.
Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

include/linux/perf_event.h

@@ -906,6 +906,13 @@ static struct perf_pmu_events_attr _var = {				\
 	.id   =  _id,							\
 };
 
+#define PMU_EVENT_ATTR_STRING(_name, _var, _str)			    \
+static struct perf_pmu_events_attr _var = {				    \
+	.attr		= __ATTR(_name, 0444, perf_event_sysfs_show, NULL), \
+	.id		= 0,						    \
+	.event_str	= _str,						    \
+};
+
 #define PMU_FORMAT_ATTR(_name, _format)					\
 static ssize_t								\
 _name##_show(struct device *dev,					\