[mbed-tls] PSA key slot management functions access private structure members

Hello,

In mbedLS v3.4.0, I came across a build error that there are no members for type and flag in psa_core_keyattributes_t structure.

The following functions in psa_crypto_core.h access private members type and flag of psa_core_keyattributes_t structure without the MBEDTLS_PRIBATE() private access.

* psa_is_key_slot_occupied() * psa_key_slot_get_flags() * psa_key_slot_set_flags() * psa_key_slot_set_bits_in_flags() * psa_key_slot_clear_bits()

Updating to private access for attribute struct members in psa_crypto_core.h fixed the build errors.

Regards, Archanaa