ARM: dts: Add reg property to regulator nodes in exynos5250-arndale

For consistency and correctness, since this is a bus, even if not
physical, it is worth to add 'reg' property and unit-address to subnodes.
The 'reg' property would merely be an index. Also for consistency, use
"regulator" as node name as used most commonly across other dts files.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>