stepper: Use a sane default for homing_positive_dir

Use the endstop position to determine a sane default for
homing_positive_dir.

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

config/makergear-m2-2012.cfg

@@ -9,12 +9,11 @@ dir_pin: !PL1
 enable_pin: !PA7
 step_distance: .0225
 endstop_pin: ^!PB6
-homing_speed: 50.0
-homing_stepper_phases: 32
-homing_endstop_accuracy: .200
-position_min: -0.25
 position_endstop: 0.0
 position_max: 200
+homing_speed: 50
+homing_stepper_phases: 32
+homing_endstop_accuracy: .200
 
 [stepper_y]
 step_pin: PC1
@@ -22,12 +21,11 @@ dir_pin: PL0
 enable_pin: !PA6
 step_distance: .0225
 endstop_pin: ^!PB5
-homing_speed: 50.0
-homing_stepper_phases: 32
-homing_endstop_accuracy: .200
-position_min: -0.25
 position_endstop: 0.0
 position_max: 250
+homing_speed: 50
+homing_stepper_phases: 32
+homing_endstop_accuracy: .200
 
 [stepper_z]
 step_pin: PC2
@@ -35,13 +33,12 @@ dir_pin: !PL2
 enable_pin: !PA5
 step_distance: .005
 endstop_pin: ^!PB4
-homing_speed: 4.0
-homing_retract_dist: 2.0
-homing_stepper_phases: 32
-homing_endstop_accuracy: .050
 position_min: 0.1
 position_endstop: 0.7
 position_max: 200
+homing_retract_dist: 2.0
+homing_stepper_phases: 32
+homing_endstop_accuracy: .070
 
 [extruder]
 step_pin: PC3