Write an all-bits-zero NV seed file for the tests. Without this, if
the seed file is not present when this test suite is executed, the
PSA module initialization will fail, causing most test cases to fail.
Also write an all-bits-zero NV seed file at the end. The test cases in
this test suite mess with the file, but subsequent test suites may
need it.
Add a function to configure entropy sources. For testing only.
Use it to test that the library initialization fails properly if there is no
entropy source.
Allow mbedtls_psa_crypto_free to be called twice, or without a prior
call to psa_crypto_init. Keep track of the initialization state more
precisely in psa_crypto_init so that mbedtls_psa_crypto_free knows
what to do.
