This changes the GL-renderer interface to pass the initial framebuffer
size and compositing area explicitly. All backends are changed to
provide the correct parameters.
GL-renderer mostly does not yet use these values, but later patches
will. The pbuffer path uses it already, because they replaced the
existing fields.
All this is to make GL-renderer aware of the different sizes, so it can
implement the future revision of the screenshooting API.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>