Boundary Devices has a tool to load directly a U-boot binary file, all using the USB OTG port. Assuming that you have connected your i.MX board to your Linux Host through an USB cable, board is power-on with dip switches configure to 'Serial Download Mode' (this configuration depends on the board you are booting), clone the imx_usb_loader repo, generate the tool then boot as indicate below:
$ cd imx_usb_loader
On the console terminal, you should see the booting kernel logs and at the end reaching the login prompt.
 Unbricking a Nitrogen6X or Sabre Lite i.MX6 board
 Boundary Devices Repos
 Boundary Devices Main page