ns16550: move CONFIG_SYS_NS16550 to Kconfig

Move CONFIG_SYS_NS16550 to Kconfig, and run moveconfig.py.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
diff --git a/configs/walnut_defconfig b/configs/walnut_defconfig
index 844e67f..29b3d2b 100644
--- a/configs/walnut_defconfig
+++ b/configs/walnut_defconfig
@@ -1,3 +1,4 @@
 CONFIG_PPC=y
 CONFIG_4xx=y
 CONFIG_TARGET_WALNUT=y
+CONFIG_SYS_NS16550=y