x86/aperfmperf: Untangle Intel and AMD frequency invariance init

AMD boot CPU initialization happens late via ACPI/CPPC which prevents the
Intel parts from being marked __init.

Split out the common code and provide a dedicated interface for the AMD
initialization and mark the Intel specific code and data __init.

The remaining text size is almost cut in half:

  text:		2614	->	1350
  init.text:	   0	->	 786

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/20220415161206.592465719@linutronix.de