atkbd attach excitement during boot

[Randy Bush]

> Humm.  It seems this wasn't the actual faulting instruction.  Can you do
> 'l *0xffffffff80704740'?

(gdb) l *0xffffffff80704740
0xffffffff80704740 is in sckbdevent (/usr/src/sys/dev/syscons/syscons.c:743).
738          * the Xaccel-2.1 keyboard hang, but it can't hurt.         XXX
739          */
740         while ((c = scgetc(sc, SCGETC_NONBLOCK)) != NOKEY) {
741
742             cur_tty = SC_DEV(sc, sc->cur_scp->index);
743             if (!tty_opened(cur_tty))
744                 continue;
745
746             if ((*sc->cur_scp->tsw->te_input)(sc->cur_scp, c, cur_tty))
747                 continue;