Add power management support in the SPD

This patch implements a set of handlers in the SPD which are called by
the PSCI runtime service upon receiving a power management
operation. These handlers in turn pass control to the Secure Payload
image if required before returning control to PSCI. This ensures that
the Secure Payload has complete visibility of all power transitions in
the system and can prepare accordingly.

Change-Id: I2d1dba5629b7cf2d53999d39fe807dfcf3f62fe2
diff --git a/services/psci/psci_private.h b/services/psci/psci_private.h
index 3d7ae74..351cbe8 100644
--- a/services/psci/psci_private.h
+++ b/services/psci/psci_private.h
@@ -96,6 +96,12 @@
 extern afflvl_power_on_finisher psci_afflvl_sus_finish_handlers[];
 
 /*******************************************************************************
+ * Weak declarations to allow PSCI to cope on a system where the Secure Payload
+ * Dispatcher is missing. An SPD will define this structure when present.
+ ******************************************************************************/
+extern const spd_pm_ops spd_pm;
+
+/*******************************************************************************
  * Function prototypes
  ******************************************************************************/
 /* Private exported functions from psci_common.c */