cmd/internal/obj/sparc64: prepare for the use of Prog.Reg
cmd/internal/obj/sparc64: prepare for the use of Prog.Reg

Change-Id: I707d32777390a4e076ce804ef2d5a5478189f1a4

4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go,4ad/go