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/ls1046ardb_sdcard_defconfig b/configs/ls1046ardb_sdcard_defconfig
index e20db0e..2281417 100644
--- a/configs/ls1046ardb_sdcard_defconfig
+++ b/configs/ls1046ardb_sdcard_defconfig
@@ -2,6 +2,7 @@
 CONFIG_TARGET_LS1046ARDB=y
 CONFIG_SYS_TEXT_BASE=0x82000000
 CONFIG_FSL_LS_PPA=y
+CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL=y
 CONFIG_DEFAULT_DEVICE_TREE="fsl-ls1046a-rdb"
 CONFIG_DISTRO_DEFAULTS=y