i2400m/USB: probe/disconnect, dev init/shutdown and reset backends

Implements probe/disconnect for the USB device, as well as main
backends for the generic driver to control the USB device
(bus_dev_start(), bus_dev_stop() and bus_reset()).
Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>