build(stm32mp1): add scripts for STM32MP13

Add the required files to compile STM32MP13 variant of STM32MP1.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I5078f6c29d962c1c7090458fd6438380587ee786
diff --git a/group/tf-l1-build-plat/stm32mp1-mp13:nil b/group/tf-l1-build-plat/stm32mp1-mp13:nil
new file mode 100644
index 0000000..0849ee7
--- /dev/null
+++ b/group/tf-l1-build-plat/stm32mp1-mp13:nil
@@ -0,0 +1,6 @@
+#
+# Copyright (c) 2022 Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+