crypto: null - 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



Change-Id: I9f879e0a86eb4a9ff08d65a2128d230ec06e0f4c
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Git-Repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-Commit: 8d605398425843c7ce3c0e9a0434d832d3bd54cc
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>