feat(unittests): add a unit test framework.

This patch adds all the infrastructure needed to run unit tests for
RMM, including a new variant for platform host, called `host_test`.

To build and run the tests:

cmake -DRMM_CONFIG=host_defcfg -DHOST_VARIANT=host_test \
  -DCMAKE_BUILD_TYPE=Debug -S ${RMM_SOURCE_DIR} -B ${RMM_BUILD_DIR}
cmake --build ${RMM_BUILD_DIR} -- run-unittests

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: If16686e111d91c563f8e7281d4ee7ca2864125ae
diff --git a/docs/readme.rst b/docs/readme.rst
index 25a7e1d..c198f72 100644
--- a/docs/readme.rst
+++ b/docs/readme.rst
@@ -64,7 +64,7 @@
 
 The TF-RMM project requires to be linked with certain other 3rd party projects
 and they are to be cloned from their repositories into ``ext`` folder before
-building. The projects are `MbedTLS`_, `t_cose`_, and `QCBOR`_.
+building. The projects are `MbedTLS`_, `t_cose`_, `QCBOR`_ and `CppUTest`_.
 
 The project also contains files which are imported from other projects
 into the source tree and may have a different license. Such files with
@@ -119,3 +119,4 @@
 .. _BSD-3-Clause License: https://tf-rmm.readthedocs.io/en/latest/about/license.html
 .. _License and Copyright for Contributions: https://tf-rmm.readthedocs.io/en/latest/process/contributing.html#license-and-copyright-for-contributions
 .. _Contributor's Guide: https://tf-rmm.readthedocs.io/en/latest/process/contributing.html
+.. _CppUTest: https://github.com/cpputest/cpputest.git