MIPS: smp: Make stop_this_cpu() actually stop the CPU

Since cpu_wait() enables interrupts upon return, CPUs which have
entered stop_this_cpu() may still end up handling interrupts.
This can lead to the softlockup detector firing on a panic or
restart/poweroff/halt. Just disable interrupts and spin to ensure
nothing else runs on the CPU once it has entered stop_this_cpu().

Signed-off-by: Andrew Bresticker <[e-mail]>
Cc: James Hogan <[e-mail]>
Cc: Maciej W. Rozycki <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Patchwork: https://patchwork.linux-mips.org/patch/9601/
Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/kernel/smp.c

···
 	 * Remove this CPU:
 	 */
 	set_cpu_online(smp_processor_id(), false);
-	for (;;) {
-		if (cpu_wait)
-			(*cpu_wait)();		/* Wait if available. */
-	}
+	local_irq_disable();
+	while (1);
 }
 
 void smp_send_stop(void)