Minimal support just for testing.
Only the window surface creation (including size determination) is
really platform specific, so this could be some generic thing with
platform-specific support as some sort of sub-driver, but on the other
hand I don't see much of a need for such a thing.
While most of the fbdev usage is done by the EGL driver, using this
fbdev ioctl is apparently the only way to get the display resolution.