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/mx6slevk_spl_defconfig b/configs/mx6slevk_spl_defconfig
index f2f44ce..7c445e6 100644
--- a/configs/mx6slevk_spl_defconfig
+++ b/configs/mx6slevk_spl_defconfig
@@ -17,7 +17,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx6sl-evk"
 CONFIG_SPL_TEXT_BASE=0x00908000
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
 # CONFIG_CMD_BMODE is not set