posix-timers: Consolidate signal queueing

Rename posix_timer_event() to posix_timer_queue_signal() as this is what
the function is about.

Consolidate the requeue pending and deactivation updates into that function
as there is no point in doing this in all incarnations of posix timers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>