USB: serial: add vizzini driver

Here's a driver for the Vizzini USB to serial device.
It looks to be copied from cdc-acm, and probably can be cleaned up a lot
more.  Also, there's some odd "try to grab another interface" that is
probably wrong.  And, if this really is a cdc-acm device, it probably
should just be a quirk of the cdc-acm device, but I can't figure that
out, and people have been using this driver for a long time now.  So
merge it to let people use their hardware and clean it up over time.

Driver written by Rob Duncan but cleaned up and forward ported to the
latest kernel tree by me.

Cc: Rob Duncan <rob.duncan@exar.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>