drm/exynos: Fix build error with exynos_drm_connector.c

exynos_drm_connector.c now uses videomode helper API. Hence select
VIDEOMODE_HELPERS at DRM_EXYNOS level itself instead of at
DRM_EXYNOS_FIMD to avoid the following compilation error when FIMD
is not selected (introduced by commit cf796235a6 "drm/exynos: fimd:
replace struct fb_videomode with videomode"):
drivers/built-in.o: In function `exynos_drm_connector_get_modes':
drivers/gpu/drm/exynos/exynos_drm_connector.c:86:
undefined reference to `drm_display_mode_from_videomode'
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/Kconfig

@@ -6,6 +6,7 @@ config DRM_EXYNOS
 	select FB_CFB_COPYAREA
 	select FB_CFB_IMAGEBLIT
 	select VT_HW_CONSOLE_BINDING if FRAMEBUFFER_CONSOLE
+	select VIDEOMODE_HELPERS
 	help
 	  Choose this option if you have a Samsung SoC EXYNOS chipset.
 	  If M is selected the module will be called exynosdrm.
@@ -26,7 +27,6 @@ config DRM_EXYNOS_FIMD
 	bool "Exynos DRM FIMD"
 	depends on DRM_EXYNOS && !FB_S3C && !ARCH_MULTIPLATFORM
 	select FB_MODE_HELPERS
-	select VIDEOMODE_HELPERS
 	help
 	  Choose this option if you want to use Exynos FIMD for DRM.