[usbdev,cw340] No USB device listed on host with Earl Grey running in CW340

I'm trying to work with the OpenTitan USB device peripheral, running Earl Grey in my CW340 FPGA.
I've tried running the `hello_usbdev` binary, the `usb_harness` test and the `usbdev_smoketest` test, and the expected USB device (VID:PID `18d1:503a` according to `sw/host/tests/chip/usb/usb.rs`) never shows up in `lsusb` on my Ubuntu host.

Not sure what I'm doing wrong here. For reference, I'm not using the Hyperdebug board or a ChipWhisperer board; I'm running `opentitantool` with `--interface=cw340` if that is relevant.

Let me know if there's any other information I can provide to help solve this. Thanks for your help in advance.

Start by comparing the CW340 setup and `opentitantool --interface=cw340` behavior with the `hello_usbdev`, `usb_harness`, and `usbdev_smoketest` runs. Check `sw/host/tests/chip/usb/usb.rs` for the expected VID/PID and use `lsusb` to establish whether the device is ever enumerated; done means identifying the cause or documenting the CW340 limitation.

Written by the indexing model from the issue text.