ARM: dts: Move display-timings node from fimd to dp in exynos5250-arndale, smdk5250 and smdk5420

This patch moves the display-timings node from fimd to dp to reflect the
device tree bindings change.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
[tomeu.vizoso@collabora.com: Rebased]
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>