This is another "gadget" driver -- one that lets user mode
code implement usb device functions, with all the classic
advantages of such solutions.  There's an example driver
at the linux-usb "gadget" web page, which uses pthreads
and handles several control requests in user mode.

This capability is packaged in the form of a filesystem,
conventionally mounted at /dev/gadget, with files that the
user mode driver opens, configures, and then uses with
normal read() and write() system calls.  Because this
doesn't require use of ioctl(), such user mode drivers
can be written in almost any language:  not just C, but
also Java, Python, Perl, and others -- likely even BASH.

For now, such user mode gadget drivers are limited to a
single configuration, although the interfaces in that
configuration could support multiple altsettings when
the hardware allows.

Please merge.  This first patch provides the driver,
the next one adds kconfig and kbuild support.