Turn the dbgtty closer to a device driver by allocating the dbc
structure in its own xhci_dbc_tty_probe() function, and freeing it
in xhci_dbc_tty_remove()

Remove xhci_do_dbc_exit() as its no longer needed.

allocate and create the dbc strcuture in xhci_dbc_tty_probe()
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220216095153.1303105-3-mathias.nyman@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>