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/integration_guide/index.rst b/docs/integration_guide/index.rst
index 821d894..75fbbac 100644
--- a/docs/integration_guide/index.rst
+++ b/docs/integration_guide/index.rst
@@ -35,7 +35,7 @@
 How to add a new platform
 *************************
 
-:doc:`Porting TF-M to a New Hardware </integration_guide/platform/porting_TFM_to_a_new_hardware>`
+:doc:`Porting TF-M to a New Hardware </integration_guide/platform/porting_tfm_to_a_new_hardware>`
 contains guidance on how to add a new platform.
 
 ***************************