[Input] Fixed GamePadState.SetAxis() implementation

GamePadState.SetAxis() receives a GamePadAxes enumeration, which is a
bitmask of the axes we wish to set. SetAxis now correctly decodes the
bitmask to apply the values we are interested in.
[SDL] Use TranslateAxis() to decode ControllerAxisEvent

SDL GameControllerAxis and GamePadAxes are not interchangeable. The
driver will now correctly interpret incoming SDL messages and update
the GamePadState for the relevant axis.