You can use a dtb file with dr_mode of peripheral for mfg tool usb device mode
Please check the device tree binding guide
kernel_imx/Documentation/devicetree/bindings/usb/fsl-usb.txt
24 - dr_mode : indicates the working mode for "fsl-usb2-dr" compatible
25 controllers. Can be "host", "peripheral", or "otg". Default to
26 "host" if not defined for backward compatibility.