imx: mx6ul_evk: select DM_SERIAL

Select DM_SERIAL

Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/configs/mx6ul_9x9_evk_defconfig b/configs/mx6ul_9x9_evk_defconfig
index a9979f6..99475ea 100644
--- a/configs/mx6ul_9x9_evk_defconfig
+++ b/configs/mx6ul_9x9_evk_defconfig
@@ -81,6 +81,7 @@
 CONFIG_DM_REGULATOR_PFUZE100=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y