cpufreq: exynos5250: Set APLL rate using CCF API

Use common clock framework (CCF) APIs to set the clock rates
instead of direct register manipulation. This now updates the
sysfs entry (cpuinfo_cur_freq) correctly which did not reflect
the correct value until now. While at it clean up the PLL s-div
parameter setting as it is handled by the PLL driver.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>