Cleanup CONFIG_SPL_SERIAL_SUPPORT migration

CONFIG_SPL_SERIAL_SUPPORT had already been migrated to Kconfig, but
existed in some include files; fix those up here.

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
diff --git a/configs/controlcenterdc_defconfig b/configs/controlcenterdc_defconfig
index 5fe18c6..92d289e 100644
--- a/configs/controlcenterdc_defconfig
+++ b/configs/controlcenterdc_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SYS_MALLOC_F_LEN=0x2000
 CONFIG_TARGET_CONTROLCENTERDC=y
+CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_SPL=y