USB: Export generic USB device driver functions

This will make it possible to implement device drivers which extend the
generic driver without needing to reimplement it.

Signed-off-by: Bastien Nocera <hadess@hadess.net>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20191016093933.693-2-hadess@hadess.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>