Staging: add aten2011 usb to serial converter driver.

Many thanks to Russell Lang <gsview@ghostgum.com.au> for his
help in getting this working on newer kernel versions and
for pointing out this driver in the first place.

Cc: Russell Lang <gsview@ghostgum.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>