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