usb: add struct usb_hub_port to store port related members.

Add struct usb_hub_port pointer port_data in the struct usb_hub and allocate
struct usb_hub_port perspectively for each ports to store private data.

Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>