Now that a hub is a driver use dev_dbg rather than plain
printf.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Make all USB devices children to the hub device they are
attached to.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Since we have a driver model we can make the hub driver a
real driver model driver. Put it into a new file to separate
the hub from the USB core stuff.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>