Add Flag for Enabling 64-bit Media DRM Server

We are ready for devices to begin migrating to a 64-bit Media DRM
Server. However, not all devices are ready to make this jump yet. A
device needs to have all of its DRM Plugins ready to run as 64-bit
before it can do this. This includes having 64-bit hardware
integrations.

So that devices can turn on 64-bit support as they get ready, I am
adding flags that can be set in a device's device.mk file. There are two
parts:

* ENABLE_MEDIADRM_64 enables building the mediadrmserver as 64-bit.

* Setting drm.64bit.enabled=true in PRODUCT_PROPERTY_OVERRIDES switches
  mediadrmserver to searching for DRM Plugins in the 64-bit directory.

Test: Validated that turning on these flags enables a 64-bit
      mediadrmserver that loads 64-bit DRM Plugins from the lib64
      directory (after setting DISABLE_TREBLE_DRM to true to load this
      code as opposed to the Legacy DRM Plugin HAL)
Bug: 36076017
Change-Id: I141cfd57ff75b40c8b0cb40a5bf1439a1ab5b766
diff --git a/media/libmedia/include/DrmPluginPath.h b/media/libmedia/include/DrmPluginPath.h
new file mode 100644
index 0000000..51ba26e
--- /dev/null
+++ b/media/libmedia/include/DrmPluginPath.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2017 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.
+ */
+
+#ifndef DRM_PLUGIN_PATH_H_
+
+#define DRM_PLUGIN_PATH_H_
+
+namespace android {
+
+const char* getDrmPluginPath();
+
+}  // namespace android
+
+#endif  // DRM_PLUGIN_PATH_H_