ARM: dts: exynos: Add ADC node to Exynos5410 and Odroid XU

Move the ADC from exynos5420.dtsi to a shared file between Exynos5410 and
Exynos542x: exynos54xx.dtsi.  Enable the ADC on Odroid XU board.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>