test_psa_constant_names.py was originally written before the split of
crypto.h into crypto_values.h and more, so it now needs to read
crypto_values.h as well.
In both generate_psa_constants.py and test_psa_constant_names.py, read
crypto_extra.h as well. We don't currently define any value there, but
it's plausible that we will one day.