Docs: Fix broken URLs where possible.

The remaining broken links are to the tickets on the deprecated Phabricator.
Those URLs shall be updated after migrating the issues to TF-M GitHub mirror.

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: I3e8715bd4affc6829785f622804fa1f89116dd41
diff --git a/docs/contributing/contributing_process.rst b/docs/contributing/contributing_process.rst
index b959868..fc35b3a 100644
--- a/docs/contributing/contributing_process.rst
+++ b/docs/contributing/contributing_process.rst
@@ -9,10 +9,8 @@
 
 - It is recommended to subscribe to `TF-M mailing list <mailing_list_>`_
   via `this page <https://lists.trustedfirmware.org/mailman3/lists/tf-m.lists.trustedfirmware.org>`_.
-- Refer to the `Roadmap
-  <https://developer.trustedfirmware.org/w/tf_m/planning>`_ or send a mail to
-  the `TF-M mailing list <mailing_list_>`_ to get the latest status and plan of
-  TF-M.
+- Refer to the :doc:`/roadmap` or send a mail to the `TF-M mailing list <mailing_list_>`_
+  to get the latest status and plan of TF-M.
 - Follow :doc:`Design Proposal Guideline </contributing/tfm_design_proposal_guideline>`
   to propose your design.
 - Follow guidelines below to prepare the patch: