clk: exynos5420: replace clock ID private enums with IDs from DT header

The patch replaces private enum clock IDs in the driver with macros provided
by the DT header.

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