com.android.mediadrm.signer is built with java_sdk_library

The com.android.mediadrm.signer is built with java_sdk_library
and api files are added by running "make update-api".
The com.android.mediadrm.signer is removed in platform.xml
since it will be made auto generation by soong when the library is
built with java_sdk_library.

Bug:77577799
Test: make -j
Test: make checkapi
Test: adb shell cmd package list libraries |\
      grep com.android.mediadrm.signer
      And check the com.android.mediadrm.signer library

Change-Id: I0e773615abe6aa8d757e489de2b9d807cd356146
diff --git a/media/lib/signer/Android.bp b/media/lib/signer/Android.bp
new file mode 100644
index 0000000..3b25787
--- /dev/null
+++ b/media/lib/signer/Android.bp
@@ -0,0 +1,21 @@
+//
+// Copyright (C) 2018 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.
+//
+
+java_sdk_library {
+    name: "com.android.mediadrm.signer",
+    srcs: ["java/**/*.java"],
+    api_packages: ["com.android.mediadrm.signer"],
+}