mx6cuboxi: migrate to DM_SERIAL

Add the needed DT overrides to enable UART in SPL.

Cc: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Tested-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Fabio Estevam <festevam@denx.de>
diff --git a/configs/mx6cuboxi_defconfig b/configs/mx6cuboxi_defconfig
index 46061f5..45bc0a6 100644
--- a/configs/mx6cuboxi_defconfig
+++ b/configs/mx6cuboxi_defconfig
@@ -47,7 +47,6 @@
 CONFIG_SPL_OF_CONTROL=y
 CONFIG_OF_LIST="imx6dl-hummingboard2-emmc-som-v15 imx6q-hummingboard2-emmc-som-v15"
 CONFIG_MULTI_DTB_FIT=y
-CONFIG_SPL_OF_PLATDATA=y
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
@@ -69,6 +68,7 @@
 CONFIG_PINCTRL_IMX6=y
 CONFIG_DM_REGULATOR=y
 CONFIG_DM_REGULATOR_FIXED=y
+CONFIG_DM_SERIAL=y
 CONFIG_MXC_UART=y
 CONFIG_DM_THERMAL=y
 CONFIG_IMX_THERMAL=y