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/sandbox_noinst_defconfig b/configs/sandbox_noinst_defconfig
index 646b532..6469260 100644
--- a/configs/sandbox_noinst_defconfig
+++ b/configs/sandbox_noinst_defconfig
@@ -7,7 +7,7 @@
 CONFIG_ENV_SIZE=0x2000
 CONFIG_SYS_MALLOC_LEN=0x2000000
 CONFIG_DEFAULT_DEVICE_TREE="sandbox"
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL_DRIVERS_MISC=y
 CONFIG_SPL_SYS_MALLOC_F_LEN=0x8000
 CONFIG_SPL=y