Clean up and tighten the device-type detection, which is based on
bcdDevice.

Don't make assumptions about unknown (future) types (currently assumed
to be either FT2232C or FT-X depending on bNumInterfaces) and instead
log an error and refuse to bind so that we can add proper support when
needed.

Note that the bcdDevice values have been provided by FTDI.
Signed-off-by: Johan Hovold <johan@kernel.org>