ARM: EXYNOS: Move cpufreq and cpuidle device registration to init_machine

As exynos_cpuidle_init() and exynos_cpufreq_init() functions have just
one line of code for registering platform devices. So we can move them
to exynos_dt_machine_init() and remove exynos_cpuidle_init() and
exynos_cpufreq_init(). This will help in reducing lines of code in
exynos.c, making it more clean.

Suggested-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>