cpupower: Move print_speed function into misc helper

The print_speed can be as a common function, and expose it into misc
helper header. Then it can be used on other helper files as well.

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