doc: Update link formats

Use docutils/Sphinx-type linking with the :ref: keyword where
possible, instead of direct links to files.

As part of this patch some external links have been updated too,
especially those that point to the TF-A docs. Some link targets
are no longer valid but can be restored after the TF-A User Guide
is split up.

Change-Id: I328d5141cf9b32471bf669bfc0191e8f6f883a48
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
Signed-off-by: Jimmy Brisson <jimmy.brisson@arm.com>
diff --git a/docs/design.rst b/docs/design.rst
index e78cb4c..e900efe 100644
--- a/docs/design.rst
+++ b/docs/design.rst
@@ -4,6 +4,8 @@
 This document provides some details about the internals of the TF-A Tests
 design. It is incomplete at the moment.
 
+.. _design_high_level_behaviour:
+
 High-Level Behaviour
 --------------------
 
@@ -165,8 +167,8 @@
 -----------------------
 
 The cold boot entry point is ``tftf_entrypoint`` (see
-``tftf/framework/aarch64/entrypoint.S``). As explained in section `Global
-overview of the TF-A tests behaviour`_, only the primary CPU is expected to
+``tftf/framework/aarch64/entrypoint.S``). As explained in
+:ref:`design_high_level_behaviour`, only the primary CPU is expected to
 execute this code.
 
 Tests can power on other CPUs using the function ``tftf_cpu_on()``. This uses
@@ -242,4 +244,4 @@
 
 *Copyright (c) 2018-2019, Arm Limited. All rights reserved.*
 
-.. _Firmware Update: https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/about/docs/firmware-update.rst
+.. _Firmware update: https://trustedfirmware-a.readthedocs.io/en/latest/components/firmware-update.html