MIPS: Add arch generic CPU hotplug

Each platform has to add support for CPU hotplugging itself by providing
suitable definitions for the cpu_disable and cpu_die of the smp_ops
methods and setting SYS_SUPPORTS_HOTPLUG_CPU.  A platform should only set
SYS_SUPPORTS_HOTPLUG_CPU once all it's smp_ops definitions have the
necessary changes.  This patch contains the changes to the dummy smp_ops
definition for uni-processor systems.

Parts of the code contributed by Cavium Inc.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/process.c

@@ -50,10 +50,15 @@
  */
 void __noreturn cpu_idle(void)
 {
+	int cpu;
+
+	/* CPU is going idle. */
+	cpu = smp_processor_id();
+
 	/* endless idle loop with no priority at all */
 	while (1) {
 		tick_nohz_stop_sched_tick(1);
-		while (!need_resched()) {
+		while (!need_resched() && cpu_online(cpu)) {
 #ifdef CONFIG_MIPS_MT_SMTC
 			extern void smtc_idle_loop_hook(void);
 
@@ -62,6 +67,12 @@ void __noreturn cpu_idle(void)
 			if (cpu_wait)
 				(*cpu_wait)();
 		}
+#ifdef CONFIG_HOTPLUG_CPU
+		if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) &&
+		    (system_state == SYSTEM_RUNNING ||
+		     system_state == SYSTEM_BOOTING))
+			play_dead();
+#endif
 		tick_nohz_restart_sched_tick();
 		preempt_enable_no_resched();
 		schedule();