armv8: start.S: Subordinate CPUs psci setup vector

As current design, only Manager CPU called armv8_setup_psci() before
jump to next stage(such as Linux Kernel), Subordinate CPUs also need
setup psci vector to handle trap request which comes from higher EL
level.

Signed-off-by: Xu Zhang <423756212@qq.com>
[trini: Guard with !CONFIG_XPL_BUILD check]
diff --git a/arch/arm/cpu/armv8/start.S b/arch/arm/cpu/armv8/start.S
index d3a8a7c..829a620 100644
--- a/arch/arm/cpu/armv8/start.S
+++ b/arch/arm/cpu/armv8/start.S
@@ -334,6 +334,9 @@
 	/*
 	 * All slaves will enter EL2 and optionally EL1.
 	 */
+#if defined(CONFIG_ARMV8_PSCI) && !defined(CONFIG_XPL_BUILD)
+        bl      psci_setup_vectors
+#endif
 	adr	x4, lowlevel_in_el2
 	ldr	x5, =ES_TO_AARCH64
 	bl	armv8_switch_to_el2