[CPUFREQ] EXYNOS: Removed useless headers and codes

This patch removes no referencing header files and cleaned up
useless code.

Signed-off-by: Jaecheol Lee <jc.lee@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Dave Jones <davej@redhat.com>