cpufreq: intel_pstate: Fix compilation for !CONFIG_ACPI

mainline inclusion
from mainline-v4.20-rc1
commit 5906056e
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=44


CVE: NA

-----------------------------------------------

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>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>