cpufreq: s3c2412: use global s3c2412_cpufreq_setrefresh

cpufreq: s3c2412: use global s3c2412_cpufreq_setrefresh

There are two identical copies of the s3c2412_cpufreq_setrefresh
function: a static one in the cpufreq driver and a global
version in iotiming-s3c2412.c.

As the function requires the use of a hardcoded register address
from a header that we want to not be visible to drivers, just
move the existing global function and add a declaration in
one of the cpufreq header files.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/20200806182059.2431-36-krzk@kernel.org
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>