clocksource/dummy_timer: Move hotplug callback after the real timers

When the dummy timer callback is invoked before the real timer callbacks,
then it tries to install that timer for the starting CPU. If the platform
does not have a broadcast timer installed the installation fails with a
kernel crash. The crash happens due to a unconditional deference of the non
available broadcast device. This needs to be fixed in the timer core code.

But even when this is fixed in the core code then installing the dummy
timer before the real timers is a pointless exercise.

Move it to the end of the callback list.

Fixes: 00c1d17 ("clocksource/dummy_timer: Convert to hotplug state machine")
Reported-and-tested-by: Mason <slash.tmp@free.fr>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Richard Cochran <rcochran@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Cc: Sebastian Frias <sf84@laposte.net>
Cc: Thibaud Cornic <thibaud_cornic@sigmadesigns.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Link: http://lkml.kernel.org/r/1147ef90-7877-e4d2-bb2b-5c4fa8d3144b@free.fr

include/linux/cpuhotplug.h

@@ -101,7 +101,6 @@ enum cpuhp_state {
 	CPUHP_AP_ARM_L2X0_STARTING,
 	CPUHP_AP_ARM_ARCH_TIMER_STARTING,
 	CPUHP_AP_ARM_GLOBAL_TIMER_STARTING,
-	CPUHP_AP_DUMMY_TIMER_STARTING,
 	CPUHP_AP_JCORE_TIMER_STARTING,
 	CPUHP_AP_EXYNOS4_MCT_TIMER_STARTING,
 	CPUHP_AP_ARM_TWD_STARTING,
@@ -115,6 +114,8 @@ enum cpuhp_state {
 	CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
 	CPUHP_AP_KVM_ARM_VGIC_STARTING,
 	CPUHP_AP_KVM_ARM_TIMER_STARTING,
+	/* Must be the last timer callback */
+	CPUHP_AP_DUMMY_TIMER_STARTING,
 	CPUHP_AP_ARM_XEN_STARTING,
 	CPUHP_AP_ARM_CORESIGHT_STARTING,
 	CPUHP_AP_ARM_CORESIGHT4_STARTING,