add virtio-console driver

This patch adds a new driver for use of virtio-console devices as
ttys.  It's still in an early state and not compiled by default, yet.
Currently it is only wired into amd64. i386 is still missing.
Discussed with uebayasi@, deraadt@

src/etc/MAKEDEV.common

@@ -1,4 +1,4 @@
-vers(a, {-$OpenBSD: MAKEDEV.common,v 1.82 2015/12/09 04:11:58 deraadt Exp $-})dnl
+vers(a, {-$OpenBSD: MAKEDEV.common,v 1.83 2015/12/21 22:15:53 sf Exp $-})dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
 dnl
@@ -383,6 +383,8 @@ _mkdev(com, {-tty[0-7][0-9a-f]-}, {-U=${i#tty*}
 	M tty$U c major_com_c $o 660 dialer uucp
 	M cua$U c major_com_c Add($o, 128) 660 dialer uucp-})dnl
 __devitem(ttyc, ttyc*, Cyclades serial ports,cy)dnl
+__devitem(ttyVI, ttyVI*, Virtio serial ports,viocon)dnl
+_mkdev(ttyVI, ttyVI*, {-M ttyVI$U c major_ttyVI_c $U 660 dialer uucp-})dnl
 __devitem(tzs, tty[a-z]*, Zilog 8530 Serial Port,zs)dnl
 _mkdev(tzs, {-tty[a-z]-}, {-u=${i#tty*}
 	case $u in

src/etc/etc.amd64/MAKEDEV.md

@@ -1,6 +1,6 @@
 define(MACHINE,amd64)dnl
 vers(__file__,
-	{-$OpenBSD: MAKEDEV.md,v 1.61 2015/11/10 21:42:28 sthen Exp $-},
+	{-$OpenBSD: MAKEDEV.md,v 1.62 2015/12/21 22:15:53 sf Exp $-},
 etc.MACHINE)dnl
 dnl
 dnl Copyright (c) 2001-2006 Todd T. Fries <todd@OpenBSD.org>
@@ -39,6 +39,7 @@ _DEV(st, 14, 5)
 _TITLE(term)
 _DEV(com, 8)
 _DEV(ttyc, 38)
+_DEV(ttyVI, 94)
 _TITLE(pty)
 _DEV(ptm, 81)
 _DEV(pty, 6)
@@ -130,5 +131,6 @@ target(all, bktr, 0)dnl
 target(all, gpio, 0, 1, 2)dnl
 target(all, nvram)dnl
 target(all, drm, 0, 1, 2, 3)dnl
+target(all, ttyVI, 00, 10, 20, 30, 40)dnl
 twrget(ramd, wsdisp, ttyC, 0)dnl
 target(ramd, fd, 0)dnl