disable arm registifier for the moment

R=ken2, ken3
CC=golang-dev
https://golang.org/cl/3970041

src/cmd/5g/reg.c

@@ -137,6 +137,7 @@ regopt(Prog *firstp)
 	uint32 vreg;
 	Bits bit;
 
+return; // disabled for the moment
 	if(first == 0) {
 		fmtinstall('Q', Qconv);
 	}