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/kontron_sl28_defconfig b/configs/kontron_sl28_defconfig
index 48ec43b..9abeacd 100644
--- a/configs/kontron_sl28_defconfig
+++ b/configs/kontron_sl28_defconfig
@@ -11,7 +11,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="fsl-ls1028a-kontron-sl28"
 CONFIG_SPL_TEXT_BASE=0x18010000
 CONFIG_SYS_FSL_SDHC_CLK_DIV=1
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL_SIZE_LIMIT=0x20000
 CONFIG_SPL_SIZE_LIMIT_PROVIDE_STACK=0x0
 CONFIG_SPL=y