drm/exynos: Select VIDEOMODE_HELPERS for FIMD

FIMD also requires video mode helper APIs.
Without this patch we get the following build error:
drivers/gpu/drm/exynos/exynos_drm_fimd.c:895: undefined reference to
`of_get_fb_videomode'
make: *** [vmlinux] Error 1
Signed-off-by: NSachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: NInki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/Kconfig

@@ -25,8 +25,8 @@ config DRM_EXYNOS_DMABUF
 config DRM_EXYNOS_FIMD
 	bool "Exynos DRM FIMD"
 	depends on OF && DRM_EXYNOS && !FB_S3C && !ARCH_MULTIPLATFORM
-	select OF_VIDEOMODE
 	select FB_MODE_HELPERS
+	select VIDEOMODE_HELPERS
 	help
 	  Choose this option if you want to use Exynos FIMD for DRM.