powerpc: Rename CONFIG_NS16550_MIN_FUNCTIONS

This symbol is specific to the PowerPC SPL implementation, so rename
this to reflect that it's in SPL and used / tested there, so that we can
then safely migrate it to Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/scripts/config_whitelist.txt b/scripts/config_whitelist.txt
index c0f55e4..3e717bb 100644
--- a/scripts/config_whitelist.txt
+++ b/scripts/config_whitelist.txt
@@ -186,7 +186,6 @@
 CONFIG_NEVER_ASSERT_ODT_TO_CPU
 CONFIG_NOBQFMAN
 CONFIG_NORBOOT
-CONFIG_NS16550_MIN_FUNCTIONS
 CONFIG_NUM_DSP_CPUS
 CONFIG_ODROID_REV_AIN
 CONFIG_OTHBOOTARGS
@@ -278,6 +277,7 @@
 CONFIG_SPI_FLASH_SIZE
 CONFIG_SPI_HALF_DUPLEX
 CONFIG_SPI_N25Q256A_RESET
+CONFIG_SPL_NS16550_MIN_FUNCTIONS
 CONFIG_SRIO1
 CONFIG_SRIO2
 CONFIG_SRIO_PCIE_BOOT_BRR_OFFSET