DELTA: Move out of the clip-zone after G28

Move down to a safe height after G28 for DELTAs.

Marlin/Marlin.h

   extern float delta_diagonal_rod_trim_tower_3;
   void calculate_delta(float cartesian[3]);
   void recalc_delta_settings(float radius, float diagonal_rod);
+  float delta_safe_distance_from_top();
   #if ENABLED(AUTO_BED_LEVELING_FEATURE)
     extern int delta_grid_spacing[2];
     void adjust_delta(float cartesian[3]);

Marlin/Marlin_main.cpp

 // Software Endstops. Default to configured limits.
 float sw_endstop_min[3] = { X_MIN_POS, Y_MIN_POS, Z_MIN_POS };
 float sw_endstop_max[3] = { X_MAX_POS, Y_MAX_POS, Z_MAX_POS };
+#if ENABLED(DELTA)
+  float delta_clip_start_height = Z_MAX_POS;
+#endif
 
 #if FAN_COUNT > 0
   int fanSpeeds[FAN_COUNT] = { 0 };
     sw_endstop_min[axis] = base_min_pos(axis) + offs;
     sw_endstop_max[axis] = base_max_pos(axis) + offs;
   }
+
   #if ENABLED(DEBUG_LEVELING_FEATURE)
     if (DEBUGGING(LEVELING)) {
       SERIAL_ECHOPAIR("For ", axis_codes[axis]);
       SERIAL_EOL;
     }
   #endif
+
+  #if ENABLED(DELTA)
+    if (axis == Z_AXIS) {
+      delta_clip_start_height = sw_endstop_max[axis] - delta_safe_distance_from_top();
+    }
+  #endif
+
 }
 
 /**
     }
   #endif
 
+  #if ENABLED(DELTA)
+    // move to a height where we can use the full xy-area
+    do_blocking_move_to_z(delta_clip_start_height);
+  #endif
+
   clean_up_after_endstop_or_probe_move();
 
   #if ENABLED(DEBUG_LEVELING_FEATURE)
     */
   }
 
+  float delta_safe_distance_from_top() {
+    float cartesian[3] = { 0 };
+    calculate_delta(cartesian);
+    float distance = delta[TOWER_3];
+    cartesian[Y_AXIS] = DELTA_PRINTABLE_RADIUS;
+    calculate_delta(cartesian);
+    return abs(distance - delta[TOWER_3]);
+  }
+
   #if ENABLED(AUTO_BED_LEVELING_FEATURE)
 
     // Adjust print surface height by linear interpolation over the bed_level array.