Pull up following revision(s) (requested by tsutsui in ticket #1001):
sys/arch/x68k/x68k/machdep.c: revision 1.187
sys/arch/x68k/x68k/locore.s: revision 1.111
sys/arch/x68k/x68k/pmap_bootstrap.c: revision 1.60
Probe extended memories before pmap_boostrap() for actual fix of PR/45915.
Also expand expected maximum extended memory regions to recognize
upto 1008 MB RAM that is supported by the XM6i emulator.
See my post on port-x68k@ for more details:
http://mail-index.NetBSD.org/port-x68k/2013/10/19/msg000039.html
Probably worth to pullup to netbsd-6.

(bouyer)