serial: 8250_dw: Fix clk-notifier/port suspend deadlock

It has been discovered that there is a potential deadlock between
the clock-change-notifier thread and the UART port suspending one:

   CPU0 (suspend CPU/UART)   CPU1 (update clock)
            ----                    ----
   lock(&port->mutex);
                             lock((work_completion)(&data->clk_work));
                             lock(&port->mutex);
   lock((work_completion)(&data->clk_work));

   *** DEADLOCK ***

The best way to fix this is to eliminate the CPU0
port->mutex/work-completion scenario. So we suggest to register and
unregister the clock-notifier during the DW APB UART port probe/remove
procedures, instead of doing that at the points of the port
startup/shutdown.

Link: https://lore.kernel.org/linux-serial/[email protected]

Fixes: cc816969d7b5 ("serial: 8250_dw: Fix common clocks usage race condition")
Reported-by: Hans de Goede <[email protected]>
Tested-by: Hans de Goede <[email protected]>
Signed-off-by: Serge Semin <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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