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_on.c b/services/std_svc/psci/psci_on.c
index 9d2295e..c8c36cd 100644
--- a/services/std_svc/psci/psci_on.c
+++ b/services/std_svc/psci/psci_on.c
@@ -67,8 +67,7 @@
  * platform handler as it can return error.
  ******************************************************************************/
 int psci_cpu_on_start(u_register_t target_cpu,
-		      entry_point_info_t *ep,
-		      unsigned int end_pwrlvl)
+		      entry_point_info_t *ep)
 {
 	int rc;
 	unsigned int target_idx = plat_core_pos_by_mpidr(target_cpu);