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/P2020RDB-PC_SDCARD_defconfig b/configs/P2020RDB-PC_SDCARD_defconfig
index f53e27b..fe3bdb2 100644
--- a/configs/P2020RDB-PC_SDCARD_defconfig
+++ b/configs/P2020RDB-PC_SDCARD_defconfig
@@ -8,7 +8,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="p2020rdb-pc"
 CONFIG_SPL_TEXT_BASE=0xf8f81000
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_MPC85xx=y
 # CONFIG_CMD_ERRATA is not set