nohz: Avoid tick's double reprogramming in highres mode

In highres mode, the tick reschedules itself unconditionally to the
next jiffies.

However while this clock reprogramming is relevant when the tick is
in periodic mode, it's not that interesting when we run in dynticks mode
because irq exit is likely going to overwrite the next tick to some
randomly deferred future.

So lets just get rid of this tick self rescheduling in dynticks mode.
This way we can avoid some clockevents double write in favourable
scenarios like when we stop the tick completely in idle while no other
hrtimer is pending.

(For the record, similar piece of code was present initially when
dynticks functionality was first added: 79bf2bb3.

But later commit fb02fbc removed this check to keep jiffies updated for
the sake of long running softirqs, but was later again reverted in
ae99286b due to spurious wakeups. However it was not entirely reverted.
The long running softirqs were asked to fix themselves.

Introducing this change again shouldn't result in 'long running softirqs'
issue discussed in fb02fbc, as tick_nohz_kick_tick() is still commented
out.)

Suggested-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>