PSA_CUSTOM_KEY_PARAMETERS_INIT macro

The default production parameters for key generation or key derivation. Calling psa_generate_key_custom() or psa_key_derivation_output_key_custom() with `custom=PSA_CUSTOM_KEY_PARAMETERS_INIT` and `custom_data_length=0` is equivalent to calling psa_generate_key() or psa_key_derivation_output_key() respectively.