MIPS: Support hard limit of cpu count (nr_cpu_ids)

On MIPS currently, only the soft limit of cpu count (maxcpus) has its
effect, this patch enable the hard limit (nr_cpus) as well. Processor
cores which greater than maxcpus and less than nr_cpus can be taken up
via cpu hotplug. The code is borrowed from X86.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7183/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/setup.c

@@ -729,6 +729,25 @@ static void __init resource_init(void)
 	}
 }
 
+#ifdef CONFIG_SMP
+static void __init prefill_possible_map(void)
+{
+	int i, possible = num_possible_cpus();
+
+	if (possible > nr_cpu_ids)
+		possible = nr_cpu_ids;
+
+	for (i = 0; i < possible; i++)
+		set_cpu_possible(i, true);
+	for (; i < NR_CPUS; i++)
+		set_cpu_possible(i, false);
+
+	nr_cpu_ids = possible;
+}
+#else
+static inline void prefill_possible_map(void) {}
+#endif
+
 void __init setup_arch(char **cmdline_p)
 {
 	cpu_probe();
@@ -752,6 +771,7 @@ void __init setup_arch(char **cmdline_p)
 
 	resource_init();
 	plat_smp_setup();
+	prefill_possible_map();
 
 	cpu_cache_init();
 }