USB: add USB test and measurement class driver

This driver was originaly written by Stefan Kopp, but massively
reworked by Greg for submission.

Thanks to Felipe Balbi <me@felipebalbi.com> for lots of work in cleaning
up this driver.

Thanks to Oliver Neukum <oliver@neukum.org> for reviewing previous
versions and pointing out problems.

Cc: Stefan Kopp <stefan_kopp@agilent.com>
Cc: Marcel Janssen <korgull@home.nl>
Cc: Felipe Balbi <me@felipebalbi.com>
Cc: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>