crypto: arm64/aes-cts-cbc - move request context data to the stack

Since the CTS-CBC code completes synchronously, there is no point in
keeping part of the scratch data it uses in the request context, so
move it to the stack instead.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>