ARM: dts: use macros in clock bindings for exynos5420

The patch replaces magic numbers with macros defined in DT header
in exynos5420 clock bindings.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>