s390x: Fix GCM setup

Rework of GCM code did not include s390x causing NULL pointer dereferences on
GCM operations other than AES-GCM on platforms that support kma.  Fix this by
a proper setup of the function pointers.

Fixes: 92c9086 ("Use separate function to get GCM functions")

Signed-off-by: Juergen Christ <jchrist@linux.ibm.com>

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from #18862)

(cherry picked from commit 48e35b9)

crypto/modes/gcm128.c

@@ -495,6 +495,11 @@ static void gcm_get_funcs(struct gcm_funcs_st *ctx)
     }
     return;
 #endif
+#if defined(__s390__) || defined(__s390x__)
+    ctx->gmult = gcm_gmult_4bit;
+    ctx->ghash = gcm_ghash_4bit;
+    return;
+#endif
 }
 
 void CRYPTO_gcm128_init(GCM128_CONTEXT *ctx, void *key, block128_f block)