configs: T4240RDB: enable DM_SERIAL

As the serial devices are configured in the device tree, enable
DM_SERIAL in the non-SPL T4240RDB defconfig.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/configs/T4240RDB_defconfig b/configs/T4240RDB_defconfig
index eddd6fb..4b63ef4 100644
--- a/configs/T4240RDB_defconfig
+++ b/configs/T4240RDB_defconfig
@@ -96,7 +96,9 @@
 CONFIG_DM_PCI_COMPAT=y
 CONFIG_PCIE_FSL=y
 CONFIG_SYS_QE_FMAN_FW_IN_NOR=y
-CONFIG_SYS_NS16550_SERIAL=y
+CONFIG_SPECIFY_CONSOLE_INDEX=y
+CONFIG_DM_SERIAL=y
+CONFIG_SYS_NS16550=y
 CONFIG_SPI=y
 CONFIG_DM_SPI=y
 CONFIG_FSL_ESPI=y