feat(ast2700): add Aspeed AST2700 build config

Add the platform build config for AST2700 SoC.

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Change-Id: Id2b5310104307cc048e240582196c4b078968d93
diff --git a/group/tf-l1-build-plat/ast2700-default:nil b/group/tf-l1-build-plat/ast2700-default:nil
new file mode 100644
index 0000000..5515958
--- /dev/null
+++ b/group/tf-l1-build-plat/ast2700-default:nil
@@ -0,0 +1,6 @@
+#
+# Copyright (c) 2023 Arm Limited. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+#
+