perf: provide sysfs_show for struct perf_pmu_events_attr

(struct perf_pmu_events_attr) is defined in include/linux/perf_event.h,
but the only "show" for it is in x86 and contains x86 specific stuff.

Make a generic one for those of us who are just using the event_str.

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>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 486e84c..58f59bd 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -897,6 +897,9 @@
 	const char *event_str;
 };
 
+ssize_t perf_event_sysfs_show(struct device *dev, struct device_attribute *attr,
+			      char *page);
+
 #define PMU_EVENT_ATTR(_name, _var, _id, _show)				\
 static struct perf_pmu_events_attr _var = {				\
 	.attr = __ATTR(_name, 0444, _show, NULL),			\