selinux: Update policies for mediadrmserver

(cherry picked from commit 23a276a2)

DRM 3rd party application with platform signature
requires the permission.

Bug: 30352348
Change-Id: Idd673506764ae435db1be8cc8c13658541ffa687

platform_app.te

@@ -45,6 +45,7 @@ allow platform_app drmserver_service:service_manager find;
 allow platform_app mediaserver_service:service_manager find;
 allow platform_app mediaextractor_service:service_manager find;
 allow platform_app mediacodec_service:service_manager find;
+allow platform_app mediadrmserver_service:service_manager find;
 allow platform_app persistent_data_block_service:service_manager find;
 allow platform_app radio_service:service_manager find;
 allow platform_app surfaceflinger_service:service_manager find;