xhci: Fixes for suspend/resume of shared HCDs.

Make sure the HCD_FLAG_HW_ACCESSIBLE flag is mirrored by both roothubs,
since it refers to whether the shared hardware is accessible.  Make sure
each bus is marked as suspended by setting usb_hcd->state to
HC_STATE_SUSPENDED when the PCI host controller is resumed.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>