drm/exynos: separate Mixer and HDMI drivers

Latest Exynos SoCs does not have Mixer IP, but they still have HDMI IP.
Their drivers should be configurable separately.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
index 09c4c6a..2c6019d 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
@@ -529,8 +529,10 @@
 #ifdef CONFIG_DRM_EXYNOS_DSI
 	&dsi_driver,
 #endif
-#ifdef CONFIG_DRM_EXYNOS_HDMI
+#ifdef CONFIG_DRM_EXYNOS_MIXER
 	&mixer_driver,
+#endif
+#ifdef CONFIG_DRM_EXYNOS_HDMI
 	&hdmi_driver,
 #endif
 #ifdef CONFIG_DRM_EXYNOS_VIDI