mips: implemented orc instructions subb, mullw, convssswb, mergebw, subssw, shrsw
mips: implemented orc instructions subb, mullw, convssswb, mergebw, subssw, shrsw

okuoku/nmosh-orc,Distrotech/orc,okuoku/nmosh-orc,mojaves/orc,MOXfiles/orc,okuoku/nmosh-orc,Distrotech/orc,mojaves/orc,ijsf/OpenWebRTC-orc,ijsf/OpenWebRTC-orc,MOXfiles/orc,ijsf/OpenWebRTC-orc,mojaves/orc,jpakkane/orc,Distrotech/orc,MOXfiles/orc,jpakkane/orc,jpakkane/orc