OvmfPkg: PlatformBdsLib: install gRootBusesConnectedProtocolGuid
    
    The explanation is in the patch titled
    
      OvmfPkg: introduce gRootBusesConnectedProtocolGuid
    
    At this point, this protocol doesn't do anything yet.
    
    Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Cc: Gerd Hoffmann <kraxel@redhat.com>
    Cc: Jordan Justen <jordan.l.justen@intel.com>
    Cc: Marcel Apfelbaum <marcel@redhat.com>
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Laszlo Ersek <lersek@redhat.com>