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/local_position_estimator/BlockLocalPositionEstimator.cpp

@@ -111,11 +111,7 @@ BlockLocalPositionEstimator::BlockLocalPositionEstimator() :
 	_ref_lon(0.0),
 	_ref_alt(0.0)
 {
-#if defined(ENABLE_LOCKSTEP_SCHEDULER)
-	_lockstep_component = px4_lockstep_register_component();
-#else
 	_sensors_sub.set_interval_ms(10); // main prediction loop, 100 hz (lockstep requires to run at full rate)
-#endif
 
 	// assign distance subs to array
 	_dist_subs[0] = &_sub_dist0;
@@ -145,11 +141,6 @@ BlockLocalPositionEstimator::BlockLocalPositionEstimator() :
 		 (_param_lpe_fusion.get() & FUSE_BARO) != 0);
 }
 
-BlockLocalPositionEstimator::~BlockLocalPositionEstimator()
-{
-	px4_lockstep_unregister_component(_lockstep_component);
-}
-
 bool
 BlockLocalPositionEstimator::init()
 {
@@ -161,7 +152,6 @@ BlockLocalPositionEstimator::init()
 	return true;
 }
 
-
 Vector<float, BlockLocalPositionEstimator::n_x> BlockLocalPositionEstimator::dynamics(
 	float t,
 	const Vector<float, BlockLocalPositionEstimator::n_x> &x,
@@ -525,8 +515,6 @@ void BlockLocalPositionEstimator::Run()
 		_xDelay.update(_x);
 		_time_last_hist = _timeStamp;
 	}
-
-	px4_lockstep_progress(_lockstep_component);
 }
 
 void BlockLocalPositionEstimator::checkTimeouts()