Move PSA_PRE_1_0_KEY_DERIVATION to crypto_struct.h
We want to make the PRF context structure depend on this flag, but
crypto_extra.h is included after crypto_struct.h and having the
option at its original place would not affect crypto_struct.h.
diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index 977b021..0e0ecb2 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -191,6 +191,17 @@
} psa_hkdf_key_derivation_t;
#endif /* MBEDTLS_MD_C */
+/*
+ * If this option is not turned on, then the function `psa_key_derivation()`
+ * is removed. And the new psa_tls12_prf_key_derivation_t context is used along
+ * with the corresponding new API.
+ *
+ * The sole purpose of this option is to make the transition to the new API
+ * smoother. Once the transition is complete it can and should be removed
+ * along with the old API and its implementation.
+ */
+#define PSA_PRE_1_0_KEY_DERIVATION
+
#if defined(MBEDTLS_MD_C)
typedef struct psa_tls12_prf_key_derivation_s
{