conf: add support for sphinx-panels

The sphinx-panels package gives the ability to render unicode based
icons as required in [1] below.

Link: [1] https://github.com/OP-TEE/optee_docs/pull/186

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/conf.py b/conf.py
index fe16fae..fbbfd18 100644
--- a/conf.py
+++ b/conf.py
@@ -42,6 +42,7 @@
     'sphinx.ext.todo',
     'sphinx.ext.viewcode',
     'sphinx.ext.graphviz',
+    'sphinx_panels',
     'sphinxcontrib.plantuml',
     'sphinx_tabs.tabs',
 ]
diff --git a/requirements.txt b/requirements.txt
index e5b281e..763c2f6 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,6 @@
-sphinx_rtd_theme
-sphinxcontrib-plantuml
-Pillow
-sphinx-tabs==3.4.1
+sphinx-rtd-theme
+sphinxcontrib-plantuml==0.24
+Pillow==9.2.0
+sphinx-tabs
+sphinx-panels==0.6.0
+sphinx==4.5.0