Add new armv8-2a-dotprod arch variant support.

This patch introduces the .mk file required to support build for the new
armv8-2a-dotprod Arm64 arch variant. The file just needs to be present
but does not require to contain anything.

Test: test-art-target on Pixel 4.

Change-Id: I4b6a1e306f9819cf31cd556351bd3e8cf08e2537

core/combo/arch/arm64/armv8-2a-dotprod.mk

@@ -0,0 +1,19 @@
+#
+# Copyright (C) 2020 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 armv8-2a-dotprod Arm64 arch
+# variant. The file just needs to be present but does not require to contain
+# anything