cpufreq: cpufreq-cpu0: use cpufreq_generic_init()

Use generic cpufreq_generic_init() routine instead of replicating the same code
here.

Cc: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>