cpupower: Add "perf" option to print AMD P-State information

Add "-c --perf" option in cpupower-frequency-info to get the performance
and frequency values for AMD P-State.

Commit message amended:
Shuah Khan <skhan@linuxfoundation.org>

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