Provide a general gn to compile all ai-related applications

ai/BUILD.gn

+# Copyright (c) 2021 Huawei Device Co., Ltd.
+# 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.
+import("//build/lite/config/component/lite_component.gni")
+
+lite_component("ai") {
+  features = [
+    "asr:asr",
+    "cv:cv",
+  ]
+}