selftests: create cpufreq kconfig fragments

For the better test coverage of cpufreq driver code these extra
configurations are needed. Enable cpufreq governors and stats.

Signed-off-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>