xhci: dbctty: split dbc tty driver registration and unregistration functions.

xhci: dbctty: split dbc tty driver registration and unregistration functions.

Split the dbc tty driver registrations function into separate
init and probe parts.

The init part will register the tty driver, and should in the future be
called from module_init().
The probe part will become the normal probe function, but for now it is
called from the init part.

The unregister function is s likewise split into remove and exit parts.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200723144530.9992-25-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>