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/services/index.rst b/docs/integration_guide/services/index.rst
index a534d6d..d92f6bf 100644
--- a/docs/integration_guide/services/index.rst
+++ b/docs/integration_guide/services/index.rst
@@ -7,11 +7,11 @@
 
     Initial Attestation <tfm_attestation_integration_guide>
     Crypto <tfm_crypto_integration_guide>
-    Internal Storage <tfm_its_integration_guide>
+    Internal Trusted Storage <tfm_its_integration_guide>
     Platform <tfm_platform_integration_guide>
     Protected Storage <tfm_ps_integration_guide>
     Adding a New Service <tfm_secure_partition_addition>
-    The manifest tool <tfm_manifest_tool_user_guide>
+    Manifest Tool <tfm_manifest_tool_user_guide>
 
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