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