Refactor debug helpers for exts and hs message

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/library/ssl_misc.h b/library/ssl_misc.h
index 8ffdccb..7c32969 100644
--- a/library/ssl_misc.h
+++ b/library/ssl_misc.h
@@ -74,6 +74,9 @@
 #define MBEDTLS_SSL_RENEGOTIATION_DONE          2   /* Done or aborted */
 #define MBEDTLS_SSL_RENEGOTIATION_PENDING       3   /* Requested (server only) */
 
+/* Faked handshake message identity for HelloRetryRequest. */
+#define MBEDTLS_SSL_TLS1_3_HS_HELLO_RETRY_REQUEST ( -MBEDTLS_SSL_HS_SERVER_HELLO )
+
 /*
  * Inernal identity of handshake extensions
  */