docs: update PSCI reference

PSCI specification reference in the documentation is updated
to point to latest specification and duplicate PSCI references are
removed.

Change-Id: I35ee365f08c557f3017af4d51f6d063a7501b27e
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/docs/getting_started/rt-svc-writers-guide.rst b/docs/getting_started/rt-svc-writers-guide.rst
index 5a4be4d..fe64558 100644
--- a/docs/getting_started/rt-svc-writers-guide.rst
+++ b/docs/getting_started/rt-svc-writers-guide.rst
@@ -314,7 +314,7 @@
 
 --------------
 
-*Copyright (c) 2014-2021, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2014-2023, Arm Limited and Contributors. All rights reserved.*
 
 .. _SMCCC: https://developer.arm.com/docs/den0028/latest
-.. _PSCI: http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
+.. _PSCI: https://developer.arm.com/documentation/den0022/latest/