timer: don't wakeup idle CPUs unnecessarily

Kick the target CPU to re-evaluate the timer wheel only if the
timer being enqueued expires before the programmed next tick
event.

Change-Id: Id467ad069db59885b680f6a8e9f65f1a172af541
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>