perf: Export perf_event_update_userpage

Export perf_event_update_userpage() so that PMU driver using them,
can be built as modules.
Acked-by: NPeter Zilstra <peterz@infradead.org>
Signed-off-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

kernel/events/core.c

@@ -4904,6 +4904,7 @@ void perf_event_update_userpage(struct perf_event *event)
 unlock:
 	rcu_read_unlock();
 }
+EXPORT_SYMBOL_GPL(perf_event_update_userpage);
 
 static int perf_mmap_fault(struct vm_fault *vmf)
 {