usb: roles: intel_xhci: Supplying software node for the role mux

The primary purpose for this node will be to allow linking
the users of the switch to it. The users will be for example
USB Type-C connectors. By supplying a reference to this
node in the software nodes representing the USB Type-C
controllers or connectors, the drivers for those devices can
access the switch.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>