Constify the pointers to eventtimer and timecounter name strings.

The need for this appears as soon as you try to set the names to something
that isn't a "quoted literal".  (I'm actually confused why quoted strings
aren't a problem as well, we must have some warning disabled.)

sys/sys/timeet.h

@@ -53,7 +53,7 @@ typedef int et_deregister_cb_t(struct eventtimer *et, void *arg);
 struct eventtimer {
 	SLIST_ENTRY(eventtimer)	et_all;
 		/* Pointer to the next event timer. */
-	char			*et_name;
+	const char		*et_name;
 		/* Name of the event timer. */
 	int			et_flags;
 		/* Set of capabilities flags: */

sys/sys/timetc.h

@@ -49,7 +49,7 @@ struct timecounter {
 		/* This mask should mask off any unimplemented bits. */
 	uint64_t		tc_frequency;
 		/* Frequency of the counter in Hz. */
-	char			*tc_name;
+	const char		*tc_name;
 		/* Name of the timecounter. */
 	int			tc_quality;
 		/*