cpupower: Introduce ACPI CPPC library

Kernel ACPI subsytem introduced the sysfs attributes for acpi cppc
library in below path:

/sys/devices/system/cpu/cpuX/acpi_cppc/

And these attributes will be used for AMD P-State driver to provide some
performance and frequency values.

Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>