ARM: imx: mx5: Convert MX53 Menlo board to DM SERIAL

Convert the board from legacy serial code to DM SERIAL.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/configs/m53menlo_defconfig b/configs/m53menlo_defconfig
index 70df2b5..a9b8a2c 100644
--- a/configs/m53menlo_defconfig
+++ b/configs/m53menlo_defconfig
@@ -109,6 +109,7 @@
 CONFIG_DM_REGULATOR_GPIO=y
 CONFIG_DM_RTC=y
 CONFIG_RTC_M41T62=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_SYSRESET=y
 CONFIG_SYSRESET_WATCHDOG=y