usb: gadget: make g_printer enumerate again
This was broken in
2e87edf49 ("usb: gadget: make g_printer use
composite").
The USB-strings were not setup properly and were not used. No function
was added which results in an empty USB config.
While fixing this, the interface number is now auto generated and not
hard coded to 0.
Cc: stable@vger.kernel.org # v3.5
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>