Undo SVN rev 183283

Do not use Giant for kbdmux(4) locking. This is wrong and apparently
causing more problems than it solves. This will re-open the issue
where interrupt handlers may race with kbdmux(4) in polling mode.
Typical symptoms include (but not limited to) duplicated and/or
missing characters when low level console functions (such as gets)
are used while interrupts are enabled (for example geli password
prompt, mountroot prompt etc.)

MFC after:	3 days

sys/dev/kbdmux/kbdmux.c

@@ -104,10 +104,10 @@ MALLOC_DEFINE(M_KBDMUX, KEYBOARD_NAME, "Keyboard multiplexor");
 
 #define KBDMUX_LOCK_DESTROY(s)
 
-#define KBDMUX_LOCK(s) \
-	mtx_lock(&Giant)
-#define KBDMUX_UNLOCK(s) \
-	mtx_unlock(&Giant)
+#define KBDMUX_LOCK(s)
+
+#define KBDMUX_UNLOCK(s)
+
 #define KBDMUX_LOCK_ASSERT(s, w)
 
 #define KBDMUX_SLEEP(s, f, d, t) \