xhci: dbgtty: use IDR to support several dbc instances.

To support systems with several xhci controllers with active
dbc on each xhci we need to use IDR to identify and give
an index to each port.

Avoid using global struct tty_driver.driver_state for storing
dbc port pointer as it won't work with several dbc ports

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220216095153.1303105-6-mathias.nyman@linux.intel.com


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