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/P1020RDB-PC_36BIT_SPIFLASH_defconfig b/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
index 8abc7ca..9ce3833 100644
--- a/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
+++ b/configs/P1020RDB-PC_36BIT_SPIFLASH_defconfig
@@ -8,7 +8,7 @@
 CONFIG_SYS_MALLOC_LEN=0x100000
 CONFIG_DEFAULT_DEVICE_TREE="p1020rdb-pc_36b"
 CONFIG_SPL_TEXT_BASE=0xf8f81000
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y