ARM: dts: add dts file for exynos5260-xyref5260 board

The patch adds the dts file for xyref5260 board which
is based on exynos5260 SoC.

Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>