video: exynos: Remove OF dependency for Exynos DP

OF dependency can be removed as the driver does not actually
depend on it at all.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>