ARM: s3c: remove obsolete s3c-cpu-freq header

The s3c-cpu-freq header was previously included by:

  ./arch/arm/mach-s3c/mach-bast.c
  ./arch/arm/mach-s3c/mach-osiris-dvs.c
  ./arch/arm/mach-s3c/mach-osiris.c
  ./include/linux/soc/samsung/s3c-cpufreq-core.h

Commit a4946a153cb9 ("ARM: s3c: remove all s3c24xx support") removes the
files in ./arch/arm/mach-s3c/; commit daf0ee583fc7 ("cpufreq: remove
s3c24xx drivers") removes the file s3c-cpufreq-core.h.

Remove this obsolete header file.

This issue was identified, as s3c-cpu-freq.h referred to the removed config
ARM_S3C_CPUFREQ.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>