add EVP_PKEY_keygen and EVP_PKEY_keygen_init for x25519/ed25519 (#3681)

* add EVP_PKEY_keygen and EVP_PKEY_keygen_init for x25519/ed25519

* add a few more bindings we'll need for X25519
diff --git a/src/_cffi_src/openssl/evp.py b/src/_cffi_src/openssl/evp.py
index 3508e74..57f0889 100644
--- a/src/_cffi_src/openssl/evp.py
+++ b/src/_cffi_src/openssl/evp.py
@@ -130,6 +130,12 @@
 
 int EVP_PKEY_cmp(const EVP_PKEY *, const EVP_PKEY *);
 
+int EVP_PKEY_keygen_init(EVP_PKEY_CTX *);
+int EVP_PKEY_keygen(EVP_PKEY_CTX *, EVP_PKEY **);
+int EVP_PKEY_derive_init(EVP_PKEY_CTX *);
+int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *, EVP_PKEY *);
+int EVP_PKEY_derive(EVP_PKEY_CTX *, unsigned char *, size_t *);
+
 int EVP_PKEY_id(const EVP_PKEY *);
 int Cryptography_EVP_PKEY_id(const EVP_PKEY *);