ARM: tegra: implement basic tegra30 clock framework

Add basic tegra30 clock framework. Not all clocks are supported yet. Mainly
clocks requiring voltage scaling are not yet implemented in this version.

Based on work by Alex Frid <afrid@nvidia.com> and
Scott Williams <scwilliams@nvidia.com>.
Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>