Re-enable the Io spac in lower memory after system reset

src/backplane.rs

@@ -137,6 +137,7 @@ impl Backplane {
     }
 
     pub fn reset(&self) {
+        self.io_at_top_16mb.store(true, Ordering::Relaxed);
         for card in &self.cards {
             card.borrow_mut().reset();
         }