parisc: Avoid stalled CPU warnings after system shutdown

Commit 73580dac7618 ("parisc: Fix system shutdown halt") introduced an endless loop for systems which don't provide a software power off function. But the soft lockup detector will detect this and report stalled CPUs after some time. Avoid those unwanted warnings by disabling the soft lockup detector.

index b76f503..4516a5b 100644
@@ -143,6 +143,8 @@ void machine_power_off(void)
 	printk(KERN_EMERG "System shut down completed.\n"
 	       "Please power this system off now.");
 
+	/* prevent soft lockup/stalled CPU messages for endless loop. */
+	rcu_sysrq_start();
 	for (;;);
 }