udeb: Add onboard_usb_dev to usb-modules

On a MT8186 Chromebook, loading the onboard_usb_dev module used to cause the USB connection to break, even if we have mounted an external USB disk or microSD card (internally through USB) as root. Consequentially, we include the module in the initramfs so that the reset happens before we mount these disks to avoid boot failures.

On a tablet-style SC7180 Chromebook, the keyboard cover dock attached through USB somehow gets reset while the installer is reloading modules to check for firmware messages, and does not start working again unless the onboard_usb_dev module is included.

To solve these problems above, include the onboard_usb_dev module in the usb-modules installer udeb.