printk: use atomic updates for klogd work

The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:

  get_random_bytes()
    warn_unseeded_randomness()
      printk_deferred()
        defer_console_output()

and can be updated from interrupt contexts, such as:

  handle_irq_event_percpu()
    __irq_wake_thread()
      wake_up_process()
        try_to_wake_up()
          select_task_rq()
            select_fallback_rq()
              printk_deferred()
                defer_console_output()

and can be updated from NMI contexts, such as:

  vprintk()
    if (in_nmi()) defer_console_output()

Therefore the atomic variant of the updating functions must be used.

Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de

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