ARM: tegra: Add CPU Operating Performance Points for Tegra20

Operating Point are specified per HW version. The OPP voltages are kept
in a separate DTSI file because some boards may not define CPU regulator
in their device-tree if voltage scaling isn't necessary, like for example
in a case of tegra20-trimslice which is outlet-powered device.

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>