Make sure to acquire proc_lock mutex on calling psignal(9) in EV_WAKEUP().

Without this, Xserver could cause panic on the DIAGNOSTIC kernel as x68k:
http://mail-index.netbsd.org/source-changes/2012/08/15/msg036632.html

sys/arch/atari/dev/event_var.h

@@ -1,4 +1,4 @@
-/*	$NetBSD: event_var.h,v 1.8 2009/03/14 14:45:56 dsl Exp $	*/
+/*	$NetBSD: event_var.h,v 1.9 2014/03/29 16:46:19 tsutsui Exp $	*/
 
 /*
  * Copyright (c) 1992, 1993
@@ -69,8 +69,11 @@ struct evvar {
 		(ev)->ev_wanted = 0; \
 		wakeup((void *)(ev)); \
 	} \
-	if ((ev)->ev_async) \
+	if ((ev)->ev_async) { \
+		mutex_enter(proc_lock); \
 		psignal((ev)->ev_io, SIGIO); \
+		mutex_exit(proc_lock); \
+	} \
 }
 
 void	ev_init(struct evvar *);