cpufreq: remove s3c24xx drivers

All s3c24xx platforms were removed, so these five drivers are all
obsolete now.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>