mx28evk: Convert to CONFIG_DM_SERIAL

The conversion to CONFIG_DM_SERIAL is mandatory, so select this option.

Signed-off-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/mx28evk_defconfig b/configs/mx28evk_defconfig
index dad8839..df0ccea 100644
--- a/configs/mx28evk_defconfig
+++ b/configs/mx28evk_defconfig
@@ -62,6 +62,6 @@
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
 CONFIG_RTC_MXS=y
-CONFIG_CONS_INDEX=0
+CONFIG_DM_SERIAL=y
 CONFIG_SPI=y
 CONFIG_USB=y