Add CPU specific power management operations

This patch adds CPU core and cluster power down sequences to the CPU specific
operations framework introduced in a earlier patch. Cortex-A53, Cortex-A57 and
generic AEM sequences have been added. The latter is suitable for the
Foundation and Base AEM FVPs. A pointer to each CPU's operations structure is
saved in the per-cpu data so that it can be easily accessed during power down
seqeunces.

An optional platform API has been introduced to allow a platform to disable the
Accelerator Coherency Port (ACP) during a cluster power down sequence. The weak
definition of this function (plat_disable_acp()) does not take any action. It
should be overriden with a strong definition if the ACP is present on a
platform.

Change-Id: I8d09bd40d2f528a28d2d3f19b77101178778685d
diff --git a/services/std_svc/psci/psci_entry.S b/services/std_svc/psci/psci_entry.S
index cc57aa1..8145012 100644
--- a/services/std_svc/psci/psci_entry.S
+++ b/services/std_svc/psci/psci_entry.S
@@ -78,6 +78,12 @@
 	bl	init_cpu_data_ptr
 
 	/* ---------------------------------------------
+	 * Initialize the cpu_ops pointer.
+	 * ---------------------------------------------
+	 */
+	bl	init_cpu_ops
+
+	/* ---------------------------------------------
 	 * Set the exception vectors
 	 * ---------------------------------------------
 	 */