cmd/compile/internal/ssa: fix generation of ppc64x rules

The files PPC64.rules and rewritePPC64.go were out of sync due to
conflicts between CL 41630 and CL 42145 (i.e. running 'go run *.go'
in the gen directory resulted in unexpected changes).

Change-Id: I1d409656b66afeab6cb9c6df9b3dcab7859caa75
Reviewed-on: https://go-review.googlesource.com/43091


Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Carlos Eduardo Seo <cseo@linux.vnet.ibm.com>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>