Move SM2 algos to SM2 specific PKEY method

Use EVP_PKEY_set_alias_type to access

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6443)
diff --git a/crypto/include/internal/sm2.h b/crypto/include/internal/sm2.h
index e0e2d75..613fa34 100644
--- a/crypto/include/internal/sm2.h
+++ b/crypto/include/internal/sm2.h
@@ -42,15 +42,15 @@
                   const char *user_id, const uint8_t *msg, size_t msg_len);
 
 /*
- * SM2 signature generation. Assumes input is an SM3 digest
+ * SM2 signature generation.
  */
-int sm2_sign(int type, const unsigned char *dgst, int dgstlen,
+int sm2_sign(const unsigned char *dgst, int dgstlen,
              unsigned char *sig, unsigned int *siglen, EC_KEY *eckey);
 
 /*
- * SM2 signature verification. Assumes input is an SM3 digest
+ * SM2 signature verification.
  */
-int sm2_verify(int type, const unsigned char *dgst, int dgstlen,
+int sm2_verify(const unsigned char *dgst, int dgstlen,
                const unsigned char *sig, int siglen, EC_KEY *eckey);