USB: xhci-hcd: Add get_resuming_ports method

This patch adds support for the new get_resuming_ports HCD method to
the xhci-hcd driver.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>