[RFA] Update OpenBSD/mips64 support

[Mark Kettenis]

   From: Eric Christopher <echristo@redhat.com>
   Date: Wed, 13 Apr 2005 15:30:53 -0700

   > +	  mips64*-openbsd*)
   > +	    mips_default_abi=N64_ABI
   > +	    ;;

   Not n32?

Nope.  OpenBSD/sgi is fully 64-bit.  Don't think it even can execute
32-bit code.

Mark