Fix use of stale power states in PSCI standby finisher

A PSCI CPU_SUSPEND request to place a CPU in retention states at power levels
higher than the CPU power level is subject to the same state coordination as a
power down state. A CPU could implement multiple retention states at a
particular power level. When exiting WFI, the non-CPU power levels may be in a
different retention state to what was initially requested, therefore each CPU
should refresh its view of the states of all power levels.

Previously, a CPU re-used the state of the power levels when it entered the
retention state. This patch fixes this issue by ensuring that a CPU upon exit
from retention reads the state of each power level afresh.

Change-Id: I93b5f5065c63400c6fd2598dbaafac385748f989
diff --git a/lib/psci/psci_private.h b/lib/psci/psci_private.h
index 4935214..b795c8e 100644
--- a/lib/psci/psci_private.h
+++ b/lib/psci/psci_private.h
@@ -192,6 +192,8 @@
 void psci_query_sys_suspend_pwrstate(psci_power_state_t *state_info);
 int psci_validate_mpidr(u_register_t mpidr);
 void psci_init_req_local_pwr_states(void);
+void psci_get_target_local_pwr_states(unsigned int end_pwrlvl,
+				      psci_power_state_t *target_state);
 int psci_validate_entry_point(entry_point_info_t *ep,
 			uintptr_t entrypoint, u_register_t context_id);
 void psci_get_parent_pwr_domain_nodes(unsigned int cpu_idx,