The new CPUIDLE driver uses the Tegra's CLK API and that driver won't
strictly depend on CONFIG_PM_SLEEP, hence add the required stubs in
order to allow compiling of the new driver with the CONFIG_PM_SLEEP=n.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>