Create a new header file psa_helpers.h and put the one helper macro
that isn't specific to PSA crypto there. Use this header file in the
ITS test suite.
Create a specific file for helper functions that are related to the
PSA API. The reason for a separate file is so that it can include
<psa/crypto.h>, without forcing this header inclusion into every test
suite. In this commit, psa_helpers.function doesn't need psa/crypto.h
yet, but this will be the case in a subsequent commit.
Move PSA_ASSERT to psa_helpers.function, since that's the sort of
things it's for.
Include "psa_helpers.function" from the PSA crypto tests.
In the ITS test, don't include "psa_helpers". The ITS tests are
meant to stand alone from the rest of the library.
