ARM: tegra: Add clk_tegra structure and helper functions

Add Tegra platform specific clock structure clk_tegra and
some helper functions for generic clock framework.

struct clk_tegra is the single strcture used for all types of
clocks. reset and cfg_ex ops moved to clk_tegra from clk_ops.

Signed-off-by: Prashant Gaikwad <pgaikwad@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>