Rename ssl_cli/srv.c

Rename ssl_cli.c and ssl_srv.c to reflect the fact
that they are TLS 1.2 specific now. Align there new
names with the TLS 1.3 ones.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index b819bba..a16c8e6 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -41,9 +41,8 @@
 #endif
 
 /* Adding guard for MBEDTLS_ECDSA_C to ensure no compile errors due
- * to guards also being in ssl_srv.c and ssl_cli.c. There is a gap
- * in functionality that access to ecdh_ctx structure is needed for
- * MBEDTLS_ECDSA_C which does not seem correct.
+ * to guards in TLS code. There is a gap in functionality that access to
+ * ecdh_ctx structure is needed for MBEDTLS_ECDSA_C which does not seem correct.
  */
 #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
 #include "mbedtls/ecdh.h"