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/mx23evk_defconfig b/configs/mx23evk_defconfig
index 1640d41..8808f20 100644
--- a/configs/mx23evk_defconfig
+++ b/configs/mx23evk_defconfig
@@ -12,7 +12,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx23-evk"
 CONFIG_SPL_TEXT_BASE=0x00001000
 CONFIG_TARGET_MX23EVK=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SYS_LOAD_ADDR=0x42000000
 CONFIG_SYS_CONSOLE_IS_IN_ENV=y