PERF: Define PeriodArray._values_for_argsort (pandas-dev#24083)

Author: qwhelan

pandas/core/arrays/period.py

@@ -828,6 +828,9 @@ def _check_timedeltalike_freq_compat(self, other):
                                     .format(cls=type(self).__name__,
                                             freqstr=self.freqstr))
 
+    def _values_for_argsort(self):
+        return self._data
+
 
 PeriodArray._add_comparison_ops()
 PeriodArray._add_datetimelike_methods()