feat(mbedTLS): add config for Realm payload with mbedTLS submodule

Add a build configuration to support testing of Realm payloads using
the mbedTLS submodule. This setup ensures that the mbedTLS repository
is cloned and available during the build, which is currently required
for executing Realm payload tests.

Change-Id: Ib7ad490be1dc51a482530dc17e342c4691ec33b7
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/group/tftf-l1-build/nil,fvp-rme:nil b/group/tftf-l1-build/nil,fvp-rme:nil
new file mode 100644
index 0000000..796740a
--- /dev/null
+++ b/group/tftf-l1-build/nil,fvp-rme:nil
@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2025, Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+
+pre_tftf_build() {
+	# Clone mbedTLS submodule
+	cd "$tftf_root"
+	git submodule update --init
+}