DELTA: Move out of the clip-zone after G28

Move down to a safe height after G28 for DELTAs.

Marlin/Marlin.h

@@ -301,6 +301,7 @@ float code_value_temp_diff();
   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]);