clk: samsung: exynos5420: add cpu clock configuration data and instantiate cpu clock

With the addition of the new Samsung specific cpu-clock type, the
arm clock can be represented as a cpu-clock type. Add the CPU clock
configuration data and instantiate the CPU clock type for Exynos5420.

Changes by Bartlomiej:
- split Exynos5420 support from the original patches
- moved E5420_[EGL,KFC]_DIV0() macros to clk-exynos5420.c

Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>