staging: usbip: userspace: usbip_bind.c: major rewrite of the implementation

Rewrite functions in terms of libsysfs, which eliminates a lot of
helper functions simplifying the file layout. Now, the two processes
taking place here, an unbind of the old driver and a bind of
usbip-host, are single functions and have been renamed along with the
controlling function. A check to see if the device is already bound to
usbip-host is now included.

Signed-off-by: matt mooney <mfm@muteddisk.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>