cpufreq: Tegra: Use cpufreq_generic_suspend()

The cpufreq core now supports suspending and resuming of cpufreq
drivers and governors during systems suspend and resume, so use
the common infrastructure instead of defining special PM notifiers
for the same thing.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Tested-by: Stephen Warren <swarren@nvidia.com>
[rjw: Changelog]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>