xhci: dbc: Don't call dbc_tty_init() on every dbc tty probe

xhci: dbc: Don't call dbc_tty_init() on every dbc tty probe

The current workaround to call the dbc_tty_init() in probe is
not working in case we have several xhci devices with dbc enabled.

dbc_tty_init() should be called only once by a module init call when
module is loaded.

until dbgtty is its own module call dbc_tty_init() from xhci
module init call.

Same is true for unloading and dbc_tty_exit()

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220216095153.1303105-5-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>