dm: exynos: Move serial to driver model

Change the Exynos serial driver to work with driver model and switch over
all relevant boards to use it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/exynos-common.h b/include/configs/exynos-common.h
index 4a4b22b..34a162d 100644
--- a/include/configs/exynos-common.h
+++ b/include/configs/exynos-common.h
@@ -20,6 +20,7 @@
 #define CONFIG_DM
 #define CONFIG_CMD_DM
 #define CONFIG_DM_GPIO
+#define CONFIG_DM_SERIAL
 
 #define CONFIG_ARCH_CPU_INIT
 #define CONFIG_DISPLAY_CPUINFO