[cgen]
* cpu/mep-c5.cpu (f-12s20): Change to signed.
(lhucpm1): Limit to C5 mach.
(dsp0,dsp1): Rewrite as aliases so that intrinsics are generated.
* cpu/mep-core.cpu (extend-cdisp10): New.
(f-cdisp10): Change to signed, use extend-cdisp10 to sign extend.