Move platform compat config to their own directory.

This prevents SystemConfig from trying to read them. Also removed ' ' prefix+postfix when creating an empty config.
Bug: 140074769
Bug: 140092095
Test: Flashed device, no more "SystemConfig: Tag compat-change is unknown..." warnings in logcat

Change-Id: I374826526fe3e4555474688b65a0be7253c6dd8c