samples: rust: add a USB driver sample

In light of the newly-added Rust abstractions for USB devices and
drivers, add a sample USB rust driver that serves both to showcase what
is currently supported, as well as be the only user of the USB
abstractions for now.

Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250825-b4-usb-v1-2-7aa024de7ae8@collabora.com


[ force USB = y for now - gregkh ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>