virtio-devices: introduce ActivationContext for device activation

Signed-off-by: Peter Oskolkov <posk@google.com>

virtio-devices/src/rng.rs

@@ -244,12 +244,13 @@ impl VirtioDevice for Rng {
         self.common.ack_features(value);
     }
 
-    fn activate(
-        &mut self,
-        mem: GuestMemoryAtomic<GuestMemoryMmap>,
-        interrupt_cb: Arc<dyn VirtioInterrupt>,
-        mut queues: Vec<(usize, Queue, EventFd)>,
-    ) -> ActivateResult {
+    fn activate(&mut self, context: crate::device::ActivationContext) -> ActivateResult {
+        let crate::device::ActivationContext {
+            mem,
+            interrupt_cb,
+            mut queues,
+            ..
+        } = context;
         self.common.activate(&queues, interrupt_cb.clone())?;
         let (kill_evt, pause_evt) = self.common.dup_eventfds();