Harmonize implementation of plan9 arm64 obj with other archs

Author: rafael2k

src/cmd/link/internal/arm64/obj.go

@@ -89,15 +89,11 @@ func archinit(ctxt *ld.Link) {
 
 	case objabi.Hplan9: /* plan 9 */
 		ld.HEADR = 32 + 8
-
-		if *ld.FlagTextAddr == -1 {
-			*ld.FlagTextAddr = 0x10000 + int64(ld.HEADR)
-		}
 		if *ld.FlagRound == -1 {
 			*ld.FlagRound = 0x10000
 		}
 		if *ld.FlagTextAddr == -1 {
-			*ld.FlagTextAddr = ld.Rnd(4096, *ld.FlagRound) + int64(ld.HEADR)
+			*ld.FlagTextAddr = ld.Rnd(0x10000, *ld.FlagRound) + int64(ld.HEADR)
 		}
 
 	case objabi.Hlinux, /* arm64 elf */