Set transcode DeviceConfigs

This is the first step in supporting server-side transcoding
flags. For now, we emulate the server side flags by setting them in
the system_server. These flags will be read by the MediaProvider to
control the transcoding behavior of apps

Bug: 169327180
Test: atest TranscodeTest

Change-Id: Ia67b2c8ff948af9dc88d8e3d8b8657ae5caccbb0