px4_work_queue: directly support SITL lockstep

- the purpose is to ensure that every WorkItem (and WorkItems scheduled
by WorkItems) is allowed to run to completion every step
 - per workqueue register a lockstep component whenever a work item is
added (if not already registered)
 - once the work queue is empty unregister component

src/modules/ekf2/EKF2.cpp

@@ -194,10 +194,6 @@ EKF2::EKF2(int instance, const px4::wq_config_t &config, int imu, int mag, bool
 
 EKF2::~EKF2()
 {
-	if (!_multi_mode) {
-		px4_lockstep_unregister_component(_lockstep_component);
-	}
-
 	perf_free(_ecl_ekf_update_perf);
 	perf_free(_ecl_ekf_update_full_perf);
 }
@@ -468,14 +464,6 @@ void EKF2::Run()
 
 		// publish ekf2_timestamps
 		_ekf2_timestamps_pub.publish(ekf2_timestamps);
-
-		if (!_multi_mode) {
-			if (_lockstep_component == -1) {
-				_lockstep_component = px4_lockstep_register_component();
-			}
-
-			px4_lockstep_progress(_lockstep_component);
-		}
 	}
 }
 

src/modules/ekf2/EKF2.hpp

@@ -224,7 +224,6 @@ private:
 	uORB::SubscriptionCallbackWorkItem _vehicle_imu_sub{this, ORB_ID(vehicle_imu)};
 
 	bool _callback_registered{false};
-	int _lockstep_component{-1};
 
 	bool _distance_sensor_selected{false}; // because we can have several distance sensor instances with different orientations
 	bool _armed{false};

src/modules/ekf2/EKF2Selector.cpp

@@ -49,8 +49,6 @@ EKF2Selector::EKF2Selector() :
 EKF2Selector::~EKF2Selector()
 {
 	Stop();
-
-	px4_lockstep_unregister_component(_lockstep_component);
 }
 
 bool EKF2Selector::Start()
@@ -326,11 +324,6 @@ void EKF2Selector::PublishVehicleAttitude(bool reset)
 
 		attitude.timestamp = hrt_absolute_time();
 		_vehicle_attitude_pub.publish(attitude);
-
-		// register lockstep component on first attitude publish
-		if (_lockstep_component == -1) {
-			_lockstep_component = px4_lockstep_register_component();
-		}
 	}
 }
 
@@ -618,8 +611,6 @@ void EKF2Selector::Run()
 			}
 		}
 	}
-
-	px4_lockstep_progress(_lockstep_component);
 }
 
 void EKF2Selector::PrintStatus()

src/modules/ekf2/EKF2Selector.hpp

@@ -173,8 +173,6 @@ private:
 	uint8_t _lat_lon_reset_counter{0};
 	uint8_t _alt_reset_counter{0};
 
-	int _lockstep_component{-1};
-
 	uORB::Subscription _parameter_update_sub{ORB_ID(parameter_update)};
 	uORB::Subscription _sensors_status_imu{ORB_ID(sensors_status_imu)};