xhci: prepare for operation w/o shared hcd

This patch prepares xhci for the following scenario:
- If either of the root hubs has no ports, then omit shared hcd
- Main hcd can be USB3 if there are no USB2 ports

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220511220450.85367-3-mathias.nyman@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>