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/db-88f6720_defconfig b/configs/db-88f6720_defconfig
index 7fb82f2..632a22f 100644
--- a/configs/db-88f6720_defconfig
+++ b/configs/db-88f6720_defconfig
@@ -13,7 +13,7 @@
 CONFIG_ENV_SECT_SIZE=0x10000
 CONFIG_DEFAULT_DEVICE_TREE="armada-375-db"
 CONFIG_SPL_TEXT_BASE=0x40004030
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_DEBUG_UART_BASE=0xf1012000
 CONFIG_DEBUG_UART_CLOCK=250000000