Document the cpsw driver. Feedback from many.

OK jsg@

src/etc/mtree/4.4BSD.dist

@@ -1,4 +1,4 @@
-#	$OpenBSD: 4.4BSD.dist,v 1.231 2013/06/02 14:11:38 florian Exp $
+#	$OpenBSD: 4.4BSD.dist,v 1.232 2013/06/06 15:30:51 bmercer Exp $
 
 /set type=dir uname=root gname=wheel mode=0755
 # .
@@ -840,6 +840,8 @@ armish
 ..
 aviion
 ..
+beagle
+..
 hp300
 ..
 hppa