Split libnu into libplatform, libamex

Going to add some ALLS stuff to libplatform and the ALLS hardware
does not contain an AMEX board.

chunihook/jvs.c

@@ -5,12 +5,12 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "amex/jvs.h"
+
 #include "board/io3.h"
 
 #include "jvs/jvs-bus.h"
 
-#include "nu/jvs.h"
-
 #include "util/dprintf.h"
 
 static void chunithm_jvs_read_switches(void *ctx, struct io3_switch_state *out);