serial: Rename SERIAL_SUPPORT to SERIAL

Rename these options so that CONFIG_IS_ENABLED can be used with them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/imx6ul_isiot_emmc_defconfig b/configs/imx6ul_isiot_emmc_defconfig
index 1d21455..8b27b8d 100644
--- a/configs/imx6ul_isiot_emmc_defconfig
+++ b/configs/imx6ul_isiot_emmc_defconfig
@@ -14,7 +14,7 @@
 CONFIG_SYS_MALLOC_LEN=0x1000000
 CONFIG_DEFAULT_DEVICE_TREE="imx6ul-isiot-emmc"
 CONFIG_SPL_TEXT_BASE=0x00908000
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
 # CONFIG_CMD_BMODE is not set