ARM: dts: exynos: Make fixed regulators always-on on Arndale5250

The fixed regulators defined for Arndale5250 boards have no control lines,
so mark them as 'always-on' to better describe the hardware and also kill
the strange messages like 'MAIN_DC: disabling' after boot.

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