xhci: move bus_state structure under the xhci_hub structure.

Move the bus_state structure under struct usb_hub.

We need a bus_state strucure for each roothub to keep track of suspend
related info for each port.
Instead of keeping an array of two bus_state structures right under
struct xhci, it makes more sense move them to the xhci_hub structure.

No functional changes.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>