ci(mbedtls): adding minimal testing for mbedtls-2.28

Currently as we are migrating from mbedtls-2.28 to mbedtls-3.3 retain
some backward minimal testing for mbedtls-2.28 until deprecated.

Plan is to remove mbedtls-2.28 support from TF-A 3.0[1] release, but
retain support until 2.9 lifetime

[1]: https://lists.trustedfirmware.org/archives/list/
tf-a@lists.trustedfirmware.org/thread/YDPOPASMGEQBCOI5TKUSD3V3J75NAT7A/

Change-Id: Ib61b79ca978c97d866780893d21f85fbada5179f
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
diff --git a/run_config/fvp-tftf.fwu.mbedtls2 b/run_config/fvp-tftf.fwu.mbedtls2
new file mode 100644
index 0000000..7632cb2
--- /dev/null
+++ b/run_config/fvp-tftf.fwu.mbedtls2
@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2023, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+# Override default mbedtls to use mbedtls-2.28
+source "$ci_root/run_config/mbedtls2.pre_tf_build"
+
+source "$ci_root/run_config/fvp-tftf.fwu"