drm/exynos: Allow DRM_EXYNOS on s5pv210.

This patch brings back possibility to use drivers depending on
DRM_EXYNOS, on Samsung S5PV210/S5PC110 series based systems.

Fixes: dbbc925b ("drm/exynos: depend on ARCH_EXYNOS for DRM_EXYNOS")
Signed-off-by: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>