ARM: dts: Add dts file for Odroid XU3 board

Add DTS for the Hardkernel Odroid XU3. The name of the DTS file is
kept the same as the vendors naming, which means it's prefixed with
exynos5422 instead of exynos5800 as the SoC name even though it
includes the exyno5800 dtsi.

Signed-off-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Kukjin Kim <kgene@kernel.org>