staging: vboxvideo: Atomic phase 2: Stop using plane->fb and crtc->*

Once we are fully atomic plane->fb will always be NULL and we also
should not access things like crtc->enabled and crt->[hw]mode.

Now that we've wired up the state object handlers, we always have a
plane_state and crtc_state so change the code referencing plane->fb and
crtc->* to use the data from the plane_state and crt_state instead.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>