Add Tegra30 clock support based on common clock framework.

Signed-off-by: Prashant Gaikwad <pgaikwad@nvidia.com>
[swarren: ensure all OF lookups return valid cookies i.e. an explicit
error pointer or valid pointer not NULL, adapt to renames in earlier
patches, fixed some checkpatch issues.]
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>