While at it, add a few comments which config options #ifdef
and #else statements refer to.

Fixes: 86d333a8 (cpufreq: intel_pstate: Add base_frequency attribute)
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>