Rover: remove some unused functions
MAVLink: added MAV_CMD_DO_SET_CAM_TRIGG_DIST
GCS_MAVLink: regenerate mavlink headers
AP_Camera: added set_trigger_distance() call
Plane: support MAV_CMD_DO_SET_CAM_TRIGG_DIST
Copter: support MAV_CMD_DO_SET_CAM_TRIGG_DIST
Rover: support MAV_CMD_DO_SET_CAM_TRIGG_DIST
Iris: Update flight modes
Iris: Set FS_BATT_VOLTAGE
AP_SpdHgtControl: added FightStage parameter to update_pitch_throttle()

will be used for special landing handling
AP_TECS: added initial flight_stage handling
HAL_SITL: fixed a warning
Plane: pass FlightStage to TECS

this will allow for better throttle and pitch control on landing
Plane: use G_Dt for acro angle integration

also cleanup some other uses of performance timing
HAL_PX4: added some UART debugging

this may help to track down USB issues