drm/exynos: fimd: move platform data parsing to separate function

The patch moves platfrom_data and device tree parsing
to separate function.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>