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/imx8mn_evk_defconfig b/configs/imx8mn_evk_defconfig
index 394ee88..24effe5 100644
--- a/configs/imx8mn_evk_defconfig
+++ b/configs/imx8mn_evk_defconfig
@@ -17,7 +17,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="imx8mn-evk"
 CONFIG_SPL_TEXT_BASE=0x912000
 CONFIG_TARGET_IMX8MN_EVK=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL_DRIVERS_MISC=y
 CONFIG_SPL=y
 CONFIG_SPL_IMX_ROMAPI_LOADADDR=0x48000000