ARM: dts: exynos: Define fixed regulators in root node for consistency in Arndale

Remove the regulators node and define fixed regulators directly under
the root node.  This makes Exynos5250 Arndale board consistent with
other Exynos boards.

Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>