psci: preserve target affinity level during suspend

This patch adds support to save and restore the target affinity level
specified during a cpu_suspend psci call. This ensures that we
traverse only through the affinity levels that we originally intended
to after resuming from suspend.

Change-Id: I0900ae49a50b496da137cfec8f158da0397ec56c
diff --git a/common/psci/psci_entry.S b/common/psci/psci_entry.S
index 6532556..a6a1a6f 100644
--- a/common/psci/psci_entry.S
+++ b/common/psci/psci_entry.S
@@ -72,7 +72,10 @@
 	 * level 0.
 	 * ---------------------------------------------
 	 */
-	bl	get_max_afflvl
+	mov	x0, x19
+	bl	get_power_on_target_afflvl
+	cmp	x0, xzr
+	b.lt	_panic
 	mov	x3, x23
 	mov	x2, x0
 	mov	x0, x19