clocksource: em_sti: Set cpu_possible_mask to fix SMP broadcast

Update the STI driver by setting cpu_possible_mask to make EMEV2
SMP work as expected together with the ARM broadcast timer.

This breakage was introduced by:

f7db706b ARM: 7674/1: smp: Avoid dummy clockevent being preferred over real hardware clock-event

Without this fix SMP operation is broken on EMEV2 since no
broadcast timer interrupts trigger on the secondary CPU cores.
Signed-off-by: Magnus Damm <damm@opensource.se>
Tested-by: Simon Horman <horms+renesas@verge.net.au>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/em_sti.c

@@ -301,7 +301,7 @@ static void em_sti_register_clockevent(struct em_sti_priv *p)
 	ced->name = dev_name(&p->pdev->dev);
 	ced->features = CLOCK_EVT_FEAT_ONESHOT;
 	ced->rating = 200;
-	ced->cpumask = cpumask_of(0);
+	ced->cpumask = cpu_possible_mask;
 	ced->set_next_event = em_sti_clock_event_next;
 	ced->set_mode = em_sti_clock_event_mode;