cpu-ppc.c: derive ppc64le assembly entry points from ppccap.c

The powerpc64le assembly implementations for certain algorithms are not
directly callable, unlike on other architectures. Therefore, they require
a small amount of preprocessing handled by some C code.

This commit adds a new file derived from OpenSSL's 'ppccap.c', which
provides the expected entry point functions.

This commit is also derived from the original ppc64 support pull request
by q66:
briansmith#819

I agree to license my contributions to each file under the terms given
at the top of each file I changed.

crypto/cpu-ppc.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2009-2018 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+/* This file is derived from ppccap.c in OpenSSL */
+
+
+
+int bn_mul_mont_int(unsigned long *rp, const unsigned long *ap, const unsigned long *bp,
+                    const unsigned long *np, const unsigned long *n0, int num);
+int bn_mul4x_mont_int(unsigned long *rp, const unsigned long *ap, const unsigned long *bp,
+                      const unsigned long *np, const unsigned long *n0, int num);
+int GFp_bn_mul_mont(unsigned long *rp, const unsigned long *ap, const unsigned long *bp,
+                const unsigned long *np, const unsigned long *n0, int num)
+{
+    if (num < 4)
+        return 0;
+
+    if ((num & 3) == 0)
+        return bn_mul4x_mont_int(rp, ap, bp, np, n0, num);
+
+    /*
+     * There used to be [optional] call to bn_mul_mont_fpu64 here,
+     * but above subroutine is faster on contemporary processors.
+     * Formulation means that there might be old processors where
+     * FPU code path would be faster, POWER6 perhaps, but there was
+     * no opportunity to figure it out...
+     */
+
+    return bn_mul_mont_int(rp, ap, bp, np, n0, num);
+}
+
+