drm/exynos/fimd: allow multiplatform configuration

The patch removes dependency on !ARCH_MULTIPLATFORM.
This dependency seems to be not longer valid.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>