video: fbdev: s3c-fb: remove dead platform code for Exynos and S5PV210 platforms

Exynos5, Exynos4 and S5PV210 platforms have been converted to
use Device Tree and Exynos DRM driver long time ago.  Remove
dead platform code for these platforms and update Kconfig
s3c-fb entry accordingly.

Acked-by: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>