crypto/elliptic: temporarily disable s390x assembly

This disables the s390x assembly. It will be re-enabled when #20215
is resolved on s390x.

Change-Id: I789eca2dd478004956107359fae98ed012f04abb
Reviewed-on: https://go-review.googlesource.com/62292
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/crypto/elliptic/p256_s390x.go

@@ -32,7 +32,10 @@ func hasVectorFacility() bool
 var hasVX = hasVectorFacility()
 
 func initP256Arch() {
-	if hasVX {
+	// Assembly implementation is temporarily disabled until issue
+	// #20215 is fixed.
+	// if hasVX {
+	if false {
 		p256 = p256CurveFast{p256Params}
 		initTable()
 		return