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/display5_defconfig b/configs/display5_defconfig
index 40d3687..731df68 100644
--- a/configs/display5_defconfig
+++ b/configs/display5_defconfig
@@ -19,7 +19,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx6q-display5"
 CONFIG_SPL_TEXT_BASE=0x00908000
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_BOOTCOUNT_BOOTLIMIT=3
 CONFIG_SYS_BOOTCOUNT_ADDR=0x020CC068
 CONFIG_SPL_SYS_MALLOC_F_LEN=0x400