When trying to boot via USB on i.MX8MN it is necessary to specify the U-Boot environment location, otherwise the boot process simply hangs. Specify the environment location when booting from USB. Tested on a imx8mn-evk. Suggested-by: Michael Nazzareno Trimarchi <michael@amarulasolutions.com> Signed-off-by: Fabio Estevam <festevam@denx.de> Tested-By: Tim Harvey <tharvey@gateworks.com>