STM32-H407 write program with USB mini cable (USB-OTG)

The reason hardware designers put the extra pads in is because they live in the real world. Chip manufacturers often claim a lot of things, especially in their 'preliminary datasheets' (power consumption figures are notoriously bad) only to drop the ball on production parts. This can be particularly important for things such as high speed termination resistors, where a wrong value can cause signal or EMC issues that you'll only discover on a finished board. Having the pads there means the hardware engineer can easily add some extra resistance if they find the design is not performing as required.

For example, the early STM32 parts were advertised as having built-in 1.5kΩ pull-up resistors on the USB lines. This was a great feature, except that it turned out all production units only had 0.81kΩ to 0.95kΩ resistors due to manufacturing issues. This would not allow a device to pass USB compliance and needed quite an extensive redesign to fix the issue.

A few extra pads and jumpers isn't really worth much compared to the costs of having to re-do a board near the end of the design cycle and this is why good hardware designers will act very conservatively on these sorts of things until they have experience that the chip manufacturer is delivering on their promises.

Related: How to get more than 100mA from a USB port

Do you have a way to force USB hardware into host mode (not OTG)? I see some kernel code here (with register bit definitions here)

/*
* Wait for the musb to set as A device to enable the
* VBUS
*/
while (musb_readb(musb->mregs, MUSB_DEVCTL) &
         MUSB_DEVCTL_BDEVICE) {

    mdelay(5);
    cpu_relax();

    if (time_after(jiffies, timeout)
          || loops-- <= 0) {
        dev_err(musb->controller,
        "configured as A device timeout");
        break;
    }
}

This is just a guess, but if you can force the controller into host mode, it might clear the BDEVICE bit in DEVCTL. The OTG spec allows a minimum of 1.1 seconds and a maximum of 30 seconds for a B device to connect before the host is allowed to turn off. I don't think plain USB includes this behavior.

If that doesn't work, you'll probably have to go through enumeration. This will require a controller IC. FTDI's programmable USB converter chips will probably do the job.