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/mx6memcal_defconfig b/configs/mx6memcal_defconfig
index f5b4c52..8514883 100644
--- a/configs/mx6memcal_defconfig
+++ b/configs/mx6memcal_defconfig
@@ -12,7 +12,7 @@
 CONFIG_TARGET_MX6MEMCAL=y
 CONFIG_SYS_MALLOC_LEN=0x4000000
 CONFIG_SPL_TEXT_BASE=0x00908000
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SUPPORT_RAW_INITRD=y
 CONFIG_SPL_USB_HOST=y