cpufreq: tegra124: do not handle the CPU rail

The Tegra124 cpufreq driver has no information to handle the Vdd-CPU
rail. So this driver shouldn't handle for the CPU clock switching from
DFLL to other PLL clocks. It was designed to work on DFLL clock only,
which handle the frequency/voltage scaling in the background.

This patch removes the driver dependency of the CPU rail, as well as not
allow it to be built as a module and remove the removal function. So it
can keep working on DFLL clock.

Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: linux-pm@vger.kernel.org
Signed-off-by: Joseph Lo <josephl@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>