ARM: local timers: reserve local_timer_register() to SMP

When running an SMP_ON_UP enabled kernel on UP, or with nosmp
passed to the kernel, we want to be able to detect that a local
timer is not going to be used (local timers are only used on
SMP platforms), so we could register it as a global timer instead.

Return -ENXIO when the above case is detected.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm/kernel/smp.c

@@ -454,6 +454,9 @@ static struct local_timer_ops *lt_ops;
 #ifdef CONFIG_LOCAL_TIMERS
 int local_timer_register(struct local_timer_ops *ops)
 {
+	if (!is_smp() || !setup_max_cpus)
+		return -ENXIO;
+
 	if (lt_ops)
 		return -EBUSY;