USB: serial: cp210x: determine fw version for CP2105 and CP2108

CP2105, CP2108 and CP2102N have vendor requests that can be used to
retrieve the firmware version. Having this information available is
essential when trying to work around buggy firmware as a recent CP2102N
regression showed.

Determine and log the firmware version also for CP2105 and CP2108
during type detection at probe.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>