Make `check_names.py` repo-specific

[davidhorstmann-arm]

At present check_names.py uses a single set of regex for allowed names in all repositories. As the repositories diverge, check_names.py should distinguish between the repos and perform different name checks for each.

Currently we would like the prefix TF_PSA_CRYPTO_ and tf_psa_crypto_ to be allowed only in the TF-PSA-Crypto repository (not in Mbed TLS). In future we may want to do other things (e.g. disallowing definitions that start with psa_ in Mbed TLS.

Definition of Done:

• check_names.py only allows TF-PSA-Crypto prefixes in the TF-PSA-Crypto repo.
• The script is refactored so as to allow other repo-specific rules to be easily added.

[gilles-peskine-arm]

“What's the expected prefix for identifiers in this project?” and “what are the subprojects of this project (and their identifier prefix)?” are questions I've also faced in #164. There, each repository defines a data structure with a prefix project_cpp_prefix.

Conceptually, this feels like the sort of thing that could be defined once per project. It would be a generalization of scripts/project_name.txt. Maybe a scripts/project_data.json?

But given that we only have two projects, and only a very small number of pieces of knowledge about each project, doing this in a structured way is probably overkill.