udev: The udev enumerator now only handles devices from the current seat

udev: Add the ability to query the current framebuffer.

This is very similar to the function that queries the primary GPU

fbdev: Hook up, and use a new function to query for a fb device

main_wayland: don't hardcode /dev/fb0 anymore

Now that the framebuffer device is queried, don't assume that the
framebuffer device is /dev/fb0