mcu: Change mcu_stepper.set_position() to take a location in millimeters

Update the set_position() method to convert from millimeters to
absolute step position.

Also, update PrinterStepper.get_homed_offset() and
mcu_stepper.get_commanded_position() to return millimeters.

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

klippy/stepper.py

@@ -99,4 +99,4 @@ class PrinterStepper:
             raise homing.EndstopError(
                 "Endstop %s incorrect phase (got %d vs %d)" % (
                     self.name, pos, self.homing_endstop_phase))
-        return delta
+        return delta * self.step_dist