uboot-imx

config_distro_bootcmd.h: Remove unnecessary magic to avoid repeated USB scans

Now that "usb start" will only start usb if not already started, we can simply
call "usb start" whenever we (may) need access to usb devices, and it will only
actually scan the bus at the first call.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>