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/k2g_evm_defconfig b/configs/k2g_evm_defconfig
index 54ce875..7a21b40 100644
--- a/configs/k2g_evm_defconfig
+++ b/configs/k2g_evm_defconfig
@@ -15,7 +15,7 @@
 CONFIG_SYS_MALLOC_LEN=0x2000000
 CONFIG_SPL_DM_SPI=y
 CONFIG_DEFAULT_DEVICE_TREE="keystone-k2g-evm"
-CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SERIAL=y
 CONFIG_SPL=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y