Docs: Refresh the Crypto service integration guide

The TF-M Crypto service integration guide needs to be
refreshed to reflect newer changes that have been
merged over time. Also, introduce some useful references,
cross-referencing when needed, plus add support in conf.py
for newer versions of Sphinx.

Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>
Change-Id: I2bcbc38e5940f042b516ab44355a7ad2354dac5f
diff --git a/docs/conf.py b/docs/conf.py
index 2a8deb5..931d39d 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -49,7 +49,7 @@
     'sphinx.ext.autosectionlabel', #Make sphinx generate a label for each section
     'sphinxcontrib.plantuml', #Add support for PlantUML drawings
     'sphinxcontrib.rsvgconverter', #Add support for SVG to PDF
-    'sphinx_tabs.tabs' #Enable tab extension in Sphinx
+    'sphinx_tabs.tabs', #Enable tab extension in Sphinx
 ]
 
 # PlantUML
@@ -157,3 +157,4 @@
      author, 'manual'),
 ]
 
+language = 'en'