Add fetch_hand_message in generic

This function is one common function in generic file, get it from
the encrypted extension and submit one patch independently.

Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index a1128ed..fa777cc 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -1490,6 +1490,14 @@
 }
 
 /*
+ * Fetch TLS 1.3 handshake message header
+ */
+int mbedtls_ssl_tls1_3_fetch_handshake_msg( mbedtls_ssl_context *ssl,
+                                       unsigned hs_type,
+                                       unsigned char **buf,
+                                       size_t *buf_len );
+
+/*
  * Write TLS 1.3 handshake message header
  */
 int mbedtls_ssl_tls13_start_handshake_msg( mbedtls_ssl_context *ssl,