timer: Don't initialize 'tvec_base' on hotplug

There is no need to call init_timers_cpu() on every CPU hotplug event,
there is not much we need to reset.

 - Timer-lists are already empty at the end of migrate_timers().
 - timer_jiffies will be refreshed while adding a new timer, after the
   CPU is online again.
 - active_timers and all_timers can be reset from migrate_timers().

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/54a1c30ea7b805af55beb220cadf5a07a21b0a4d.1427814611.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>