xhci: factor out parts of xhci_gen_setup()

Factoring out parts of xhci_gen_setup() has two motivations:
- When adding functionaliy to omit shared hcd if not needed in a
  subsequent patch, we'll have to call xhci_hcd_init_usb3_data()
  from two places.
- It reduces size of xhci_gen_setup() and makes it better readable.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220511220450.85367-2-mathias.nyman@linux.intel.com


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