configs: verdin-imx8mm: verdin-imx8mp: enable dm serial

Enable driver model for serial.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
diff --git a/configs/verdin-imx8mm_defconfig b/configs/verdin-imx8mm_defconfig
index a68cae7..94ba1f5 100644
--- a/configs/verdin-imx8mm_defconfig
+++ b/configs/verdin-imx8mm_defconfig
@@ -98,6 +98,7 @@
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_FIXED=y
 CONFIG_DM_REGULATOR_GPIO=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_SYSRESET=y
 CONFIG_SPL_SYSRESET=y