stepper_enable: Move motor_off() logic to stepper_enable.py

Directly disable all the stepper motors on a global motor_off() from
the StepperEnable() class in stepper_enable.py.  This simplifies the
toolhead and kinematic classes.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/stepper.py

@@ -72,6 +72,7 @@ class PrinterStepper:
         mcu_stepper.setup_step_distance(step_dist)
         # Enable pin handling
         stepper_enable = printer.try_load_module(config, 'stepper_enable')
+        stepper_enable.register_stepper(self)
         mcu_stepper.add_active_callback(self._stepper_active)
         self.enable = lookup_enable_pin(ppins, config.get('enable_pin', None))
         # Register STEPPER_BUZZ command