ARM: timer-sp: Set dynamic irq affinity

When a cpu goes to a deep idle state where its local timer is shutdown, it
notifies the time frame work to use the broadcast timer instead.

Unfortunately, the broadcast device could wake up any CPU, including an idle one
which is not concerned by the wake up at all.

This implies, in the worst case, an idle CPU will wake up to send an IPI to
another idle cpu.

This patch fixes this for ARM platforms using timer-sp, by setting
CLOCK_EVT_FEAT_DYNIRQ feature.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>