gss_krb5: Remove VLA usage of skcipher

In the quest to remove all stack VLA usage from the kernel[1], this
replaces struct crypto_skcipher and SKCIPHER_REQUEST_ON_STACK() usage
with struct crypto_sync_skcipher and SYNC_SKCIPHER_REQUEST_ON_STACK(),
which uses a fixed stack size.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com



Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: YueHaibing <yuehaibing@huawei.com>
Cc: linux-nfs@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Git-Commit: e9e575b8f29445bcde67f421891efa4d6527d987
Git-Repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Change-Id: Ic0dedbad6e5726479e2f58c5daa773efe7c7d82e
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>