ARM: dts: Add node labels to exynos5420

Adding labels to nodes which do not have it yet in exynos5420.
This is done so as to use reference based node updation in board
files.

Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>