toolchain: change default emulation for mips64 (octeon) to n64

toolchain: change default emulation for mips64 (octeon) to n64

fixes several ld errors reported by buildbot:
http://buildbot.openwrt.org:8010/broken_packages/octeon/mdnsresponder/compile.txt
http://buildbot.openwrt.org:8010/broken_packages/octeon/luasocket/compile.txt
http://buildbot.openwrt.org:8010/broken_packages/octeon/luasec/compile.txt
http://buildbot.openwrt.org:8010/broken_packages/octeon/openvswitch/compile.txt
http://buildbot.openwrt.org:8010/broken_packages/octeon/prosody/compile.txt

link error:
 ABI is incompatible with that of the selected emulation

found at OE toolchain for bintils 2.22:
http://patchwork.openembedded.org/patch/28033/

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>
SVN-Revision: 45666