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/imx8mm_evk_defconfig b/configs/imx8mm_evk_defconfig
index dacb2c5..021a7b1 100644
--- a/configs/imx8mm_evk_defconfig
+++ b/configs/imx8mm_evk_defconfig
@@ -16,7 +16,7 @@
 CONFIG_SPL_TEXT_BASE=0x7E1000
 CONFIG_TARGET_IMX8MM_EVK=y
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL_DRIVERS_MISC=y
 CONFIG_SPL=y
 CONFIG_DISTRO_DEFAULTS=y