x86/aperfmperf: Restructure arch_scale_freq_tick()

Preparation for sharing code with the CPU frequency portion of the
aperf/mperf code.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20220415161206.706185092@linutronix.de