Exynos: Add missing dependency

CPU_FREQ_TABLE depends on CPU_FREQ. Selecting CPU_FREQ_TABLE without checking
for dependencies gives the following compilation warnings:
warning: (ARCH_TEGRA_2x_SOC && ARCH_TEGRA_3x_SOC && UX500_SOC_DB8500 &&
CPU_THERMAL && EXYNOS_THERMAL) selects CPU_FREQ_TABLE which has unmet
direct dependencies (ARCH_HAS_CPUFREQ && CPU_FREQ)

Based-on-patch-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>