Fix remote GraphicBuffer allocation in SurfaceFlinger.

This change fixes a horrible hack that I did to allow application
processes to create GraphicBuffer objects by making a binder call to
SurfaceFlinger.  This change introduces a new binder interface
specifically for doing this, and does it in such a way that
SurfaceFlinger will maintain a reference to the buffers until the app is
done with them.

Change-Id: Icb240397c6c206d7f69124c1497a829f051cb49b