px4_module: use px4_atomic_t

src/drivers/batt_smbus/batt_smbus.cpp

src/drivers/heater/heater.cpp

src/drivers/px4fmu/fmu.cpp

src/drivers/rc_input/RCInput.cpp

src/modules/events/send_event.cpp

src/modules/land_detector/LandDetector.cpp

src/modules/load_mon/load_mon.cpp

src/modules/wind_estimator/wind_estimator_main.cpp

src/platforms/px4_module.h