makes timer more consistent accros tx and nx

Also adds nx_port for user defines

port/moonlight/hwtimer.h

@@ -15,7 +15,7 @@
 #include "platform.h"
 
 #define TICKNUM_PER_SECOND 32768
-#define TICKNUM_PER_TIMER (TICKNUM_PER_SECOND / 1000)
+#define TICKNUM_PER_TIMER (TICKNUM_PER_SECOND / 1000) // ~ 1ms timer
 
 static inline int hwtimer_init(void) {
     uint64_t time = get_aclint_mtime(aclint);