Mention TF-PSA-Crypto version updates in the Mbed TLS changelog

[gilles-peskine-arm]

Mbed TLS effectively includes TF-PSA-Crypto, so it changelog should effectively include the TF-PSA-Crypto changelog.

I don't think it would make sense to replicate the content, but ChangeLog in Mbed TLS should tell users to look at tf-psa-crypto/ChangeLog.

Additionally, in Mbed TLS releases, I think we should indicate the corresponding version of TF-PSA-Crypto.

For example, we could put this entry in the changelog of Mbed TLS 4.1.0:

Submodules
   * Upgraded TF-PSA-Crypto from 1.0.0 to 1.1.0. See tf-psa-crypto/ChangeLog.

Definition of done:

• ChangeLog contains a reference to tf-psa-crypto/ChangeLog.
• A process is in place so that releases of Mbed TLS have an indication of the bundled version of TF-PSA-Crypto. This may be part of the manual release process, or automated in framework/scripts/prepare_release.py.
• Whatever structure we add is supported by framework/scripts/assemble_changelog.py.