drm: wire poll_hotplug into IRQ event thread

When handle_irq() returns Ok(None) (no IRQ event received),
also call poll_hotplug() to detect connector changes via
HPD register polling fallback. Events are fed through the
same event channel to the scheme handler.

local/recipes/gpu/redox-drm/source/src/main.rs

@@ -83,7 +83,20 @@ fn run(daemon: daemon::Daemon) -> Result<()> {
                     break;
                 }
             }
-            Ok(None) => {}
+            Ok(None) => {
+                match irq_driver.poll_hotplug() {
+                    Ok(Some(event)) => {
+                        if event_tx.send(event).is_err() {
+                            error!("redox-drm: event consumer dropped, stopping IRQ event thread");
+                            break;
+                        }
+                    }
+                    Ok(None) => {}
+                    Err(e) => {
+                        error!("redox-drm: hotplug poll error: {}", e);
+                    }
+                }
+            }
             Err(e) => {
                 error!("redox-drm: IRQ handler error: {}", e);
             }