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/devkit3250_defconfig b/configs/devkit3250_defconfig
index 1d089bd..2d4d665 100644
--- a/configs/devkit3250_defconfig
+++ b/configs/devkit3250_defconfig
@@ -12,7 +12,7 @@
 CONFIG_ENV_OFFSET=0xA0000
 CONFIG_SYS_MALLOC_LEN=0x100000
 CONFIG_SPL_TEXT_BASE=0x00000000
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SYS_LOAD_ADDR=0x80008000
 CONFIG_BOOTDELAY=1