At present USB devices with no driver model driver cannot be seen in the
device list, and we fail to set them up correctly. This means they cannot
be used.

While having real drivers that support driver model for all USB devices
is the eventual goal, we are not there yet.

As a stop-gap, add a generic USB driver which is bound when we do not have
a real driver. This allows the device to be set up and shown on the bus.
It also allows ad-hoc code (such as usb_ether) to find these devices and
set them up.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Vasut <marex@denx.de>