docs: update links to tf.org-wide process documents

tf.org-wide documents have been migrated away from
developer.trustedfirmware.org, because the latter will be
decomissioned at some point in the future. These documents are now
hosted in a new 'tf_docs' repository hosted on Github [1] and can be
easily browsed through a new ReadTheDocs website at [2].

Update all relevant links in TF-A documentation to refer to [2].

[1] https://github.com/TrustedFirmware/tf_docs
[2] https://trusted-firmware-docs.readthedocs.io/

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: Ib9d39c36250a05754fe5e46cb6f3044ecb776534
diff --git a/docs/process/maintenance.rst b/docs/process/maintenance.rst
index 45aada2..5ee435e 100644
--- a/docs/process/maintenance.rst
+++ b/docs/process/maintenance.rst
@@ -51,5 +51,5 @@
    and update the list of maintainers on the :ref:`Project
    Maintenance<maintainers>` page.
 
-.. _trustedfirmware.org Project Maintenance Process: https://developer.trustedfirmware.org/w/collaboration/project-maintenance-process/
-.. _here: https://developer.trustedfirmware.org/w/collaboration/project-maintenance-process/#how-to-become-a-maintainer
+.. _trustedfirmware.org Project Maintenance Process: https://trusted-firmware-docs.readthedocs.io/en/latest/generic_processes/project_maintenance_process.html
+.. _here: https://trusted-firmware-docs.readthedocs.io/en/latest/generic_processes/project_maintenance_process.html#how-to-become-a-maintainer