sha3: revert alignment optimization on ppc64

A previous fix to improve performance based on alignment
to sha3 was made in both ppc64le and ppc64, when it should
have only applied to ppc64le.  This changes the build tags
so it is only done for ppc64le.

Fixes golang/go#15392

Change-Id: Idf32a0370f3c76fc2b54a2897a668acbae5d43c5
Reviewed-on: https://go-review.googlesource.com/22323
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

sha3/xor.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!386,!ppc64,!ppc64le appengine
+// +build !amd64,!386,!ppc64le appengine
 
 package sha3
 

sha3/xor_unaligned.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64 386 ppc64 ppc64le
+// +build amd64 386 ppc64le
 // +build !appengine
 
 package sha3