ARM: ux500: cpuidle: replace for_each_online_cpu by for_each_possible_cpu

All the drivers are using, in their initialization function, the
for_each_possible_cpu macro.

Using for_each_online_cpu means the driver must handle the initialization
of the cpuidle device when a cpu is up which is not the case here.

Change the macro to for_each_possible_cpu as that fix the hotplug
initialization and make the initialization routine consistent with the
rest of the code in the different drivers.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>