PM / devfreq: tegra: Move governor registration to driver's probe

There is no need to register the ACTMON's governor separately from
the driver, hence let's move the registration into the driver's probe
function for consistency and to make code cleaner a tad.

Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>