cpufreq: tegra186: Simplify cluster information lookup

The CPUFREQ driver framework references each individual CPUs when
getting and setting the speed. Tegra186 has 3 clusters of A57 CPUs and
1 cluster of Denver CPUs. Hence, the Tegra186 CPUFREQ driver need to
know which cluster a given CPU belongs to. The logic in the Tegra186
driver can be greatly simplified by storing the cluster ID associated
with each CPU in the tegra186_cpufreq_cpu structure. This allow us to
completely remove the Tegra cluster info structure from the driver and
simplifiy the code.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>