SEAndroid: Allow dumping of frames from SurfaceFlinger

1. Define a common file type to be used by multiple display processes
   that need access to /data/misc/display to write data e.g. config
   files, dumped frames, etc.
2. Add policy to enable dumping frames from SurfaceFlinger process

Change-Id: I283778e0cf223c8dad8139ea99e19661aeac5d4f