1. Raise an exception when creating a USB device when host isn't
initialized.
2. Mark RP2040 dtcm_bss as NOLOAD since it doesn't need to be
loaded (just zeroed.)
3. Fix submodule location for ulab to Jeff's copy.
This allows you to list and explore connected USB devices. It
only stubs out the methods to communicate to endpoints. That will
come in a follow up once TinyUSB has it. (It's in progress.)
Related to #5986
