clk: tegra: No 7.1 super clk dividers on Tegra20

Unlike Tegra30, Tegra20 does not have a 7.1 divider for the CPU superclk.
Remove the clocks related to the divider.

Signed-off-by: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>