AP_Compass: AK8963 compass (as a part of MPU9250) support

Conflicts:
	APMrover2/APMrover2.pde
	ArduCopter/ArduCopter.pde
	ArduPlane/ArduPlane.pde
	libraries/AP_HAL/AP_HAL_Boards.h

Adapted by Víctor Mayoral Vilches (@vmayoral).
Fix feenableexcept issue
AP_Compass: Changes in compass for AK8963