ARM: tegra: clock: Drop CPU dvfs

The existing version did not extend well to core dvfs, drop it
for now until the new clk api with clk_prepare and clk_unprepare
is ready and non-atomic clocks are possible.

Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Colin Cross <ccross@android.com>