drag chain mount for TronXY P802D printer

Edited the file for fitment issues and clearance on TronXY P802D variant 3d printer. It is closer in make to a Prusa i3 style printer. The 802D model has a tighter tolerance between the allthread and the frame mount of the stepper motor. Also note the mount for the upper cable should be mounted using only the rear screw holes in the bed bracket and the front screw holes on the bed itself.