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_SECURE_BOOT_defconfig b/configs/ls1046ardb_sdcard_SECURE_BOOT_defconfig
index 196a000..04861b7 100644
--- a/configs/ls1046ardb_sdcard_SECURE_BOOT_defconfig
+++ b/configs/ls1046ardb_sdcard_SECURE_BOOT_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SYS_TEXT_BASE=0x82000000
 CONFIG_SECURE_BOOT=y
 CONFIG_FSL_LS_PPA=y
+CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL=y
 CONFIG_DEFAULT_DEVICE_TREE="fsl-ls1046a-rdb"
 CONFIG_DISTRO_DEFAULTS=y