psa: free RNG implementation before checking for remaining open key slots

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

include/psa/crypto_extra.h

@@ -193,6 +193,15 @@ psa_status_t mbedtls_psa_register_se_key(
 
 /**@}*/
 
+/**
+ * \brief PSA random deinitialization.
+ *
+ * This function frees the RNG implementation used by PSA.
+ *
+ * This is an Mbed TLS extension.
+ */
+void mbedtls_psa_random_free(void);
+
 /**
  * \brief Library deinitialization.
  *