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/brppt1_mmc_defconfig b/configs/brppt1_mmc_defconfig
index 8221221..ba971a4 100644
--- a/configs/brppt1_mmc_defconfig
+++ b/configs/brppt1_mmc_defconfig
@@ -13,7 +13,7 @@
 CONFIG_AM33XX=y
 CONFIG_TARGET_BRPPT1=y
 CONFIG_SPL_MMC=y
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_ENV_OFFSET_REDUND=0x50000
 # CONFIG_EXPERT is not set