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/mx28evk_nand_defconfig b/configs/mx28evk_nand_defconfig
index 7985c47..17f5ba4 100644
--- a/configs/mx28evk_nand_defconfig
+++ b/configs/mx28evk_nand_defconfig
@@ -10,7 +10,7 @@
 CONFIG_IMX_CONFIG=""
 CONFIG_SPL_TEXT_BASE=0x00001000
 CONFIG_TARGET_MX28EVK=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_ENV_OFFSET_REDUND=0x380000
 CONFIG_SYS_LOAD_ADDR=0x42000000