ARM: dts: Clean up exynos5250-arndale

Use the new style of referencing inherited nodes, use symbolic names,
tidy indentation and reorder includes.

Goal is the alignment of all exynos5250 based device trees for
comparison.
Signed-off-by: NAndreas Faerber <afaerber@suse.de>
Reviewed-by: NTomasz Figa <t.figa@samsung.com>
[kgene.kim@samsung.com: rebased]
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>