timers: Move trigger_dyntick_cpu() to enqueue_timer()

Consolidate the code by calling trigger_dyntick_cpu() from
enqueue_timer() instead of calling it from all its callers.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200717140551.29076-5-frederic@kernel.org