doc: Fix broken external links

Using Sphinx linkcheck on the TF-A docs revealed some broken
or permanently-redirected links. These have been updated where
possible.

Change-Id: Ie1fead47972ede3331973759b50ee466264bd2ee
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/plat/hikey960.rst b/docs/plat/hikey960.rst
index 7900b6d..7ddb0b1 100644
--- a/docs/plat/hikey960.rst
+++ b/docs/plat/hikey960.rst
@@ -189,4 +189,4 @@
 
 -  Reference `link <https://github.com/96boards-hikey/tools-images-hikey960/blob/master/build-from-source/README-ATF-UEFI-build-from-source.md>`__
 
-.. _link: http://www.96boards.org/documentation/ConsumerEdition/HiKey960/README.md
+.. _link: https://www.96boards.org/documentation/consumer/hikey/hikey960