probe: Initial support for Z-Probe hardware

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

klippy/cartesian.py

@@ -26,8 +26,12 @@ class CartKinematics:
         self.steppers[1].set_max_jerk(max_halt_velocity, max_accel)
         self.steppers[2].set_max_jerk(
             min(max_halt_velocity, self.max_z_velocity), max_accel)
-    def get_steppers(self):
+    def get_steppers(self, flags=""):
+        if flags == "Z":
+            return [self.steppers[2]]
         return list(self.steppers)
+    def get_position(self):
+        return [s.mcu_stepper.get_commanded_position() for s in self.steppers]
     def set_position(self, newpos):
         for i in StepList:
             self.steppers[i].set_position(newpos[i])