ARM: dts: add pinctrl for i2c-arbitrator of exynos5250-snow

Added i2c-arbitrator pinctrl node to Snow board.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>