Add armv8-a-branchprot arch variant

This empty file is required to be present.

Test: fvp_mini-eng* builds and boots on FVP

*: with TARGET_ARCH_VARIANT := armv8-a-branchprot

Change-Id: I689033f16663822e263f45ab5e46c9f120c9dca0

core/combo/arch/arm64/armv8-a-branchprot.mk

@@ -0,0 +1,19 @@
+#
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# .mk file required to support build for the new armv8-a-branchprot Arm64 arch
+# variant. The file just needs to be present but does not require to contain
+# anything