feat(st): add the TRUSTED_BOARD_BOOT build config

Add the TRUSTED_BOARD_BOOT option for the STM32MP15 and
STM32MP13 boards.
It will includes the specific files to manage authentication
and decryption.
Add two specific STM32MP13 configurations to use ECDSA Brainpool
algorithms.

Signed-off-by: Lionel Debieve <lionel.debieve@foss.st.com>
Change-Id: I25e79b79e8cee067524fece148c4cb3a5c79d7f0
diff --git a/group/tf-l1-build-plat/stm32mp1-tbb:nil b/group/tf-l1-build-plat/stm32mp1-tbb:nil
new file mode 100644
index 0000000..37b17ff
--- /dev/null
+++ b/group/tf-l1-build-plat/stm32mp1-tbb:nil
@@ -0,0 +1,6 @@
+#
+# Copyright (c) 2019-2022 Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+