Remove unused argument in psci_cpu_on_start()

The "end power level" value passed as the 3rd argument to the
psci_cpu_on_start() function is not used so this patch removes it.

Change-Id: Icaa68b8c4ecd94507287970455fbff354faaa41e
diff --git a/services/std_svc/psci/psci_private.h b/services/std_svc/psci/psci_private.h
index 4b91ad5..8a671b3 100644
--- a/services/std_svc/psci/psci_private.h
+++ b/services/std_svc/psci/psci_private.h
@@ -203,8 +203,7 @@
 
 /* Private exported functions from psci_on.c */
 int psci_cpu_on_start(unsigned long target_cpu,
-		      entry_point_info_t *ep,
-		      unsigned int end_pwrlvl);
+		      entry_point_info_t *ep);
 
 void psci_cpu_on_finish(unsigned int cpu_idx,
 			psci_power_state_t *state_info);