Allow the timer core to change the smp affinity of the broadcast timer
irq by setting CLOCK_EVT_FEAT_DYNIRQ flag.

This reduces interrupt pressure and wakeups on CPU0 as well as vastly
reducing the number of timer broadcast IPIs.
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>