ARM: tegra: Add ACTMON support on Tegra30

Add support for ACTMON on Tegra30. This is used to monitor activity from
different components. Based on the collected statistics, the rate at
which the external memory needs to be clocked can be derived.

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