PM / devfreq: Add devm_devfreq_add_governor()

Add resource-managed variant of devfreq_add_governor().

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>