arm: async changes

- more tracing
- pending resume() notifications
- idle function returns bool (useful for testing)

may not build (more stuff coming in later commits)

arm/main.cc

@@ -60,6 +60,7 @@ int main() {
         if ((cnt++ % 100000) == 0) {
             ToggleLed(0);
         }
+        return false;
     });
     // should never get here
 }