crypto: arm64/aes-blk - expose AES-CTR as synchronous cipher as well

In addition to wrapping the AES-CTR cipher into the async SIMD wrapper,
which exposes it as an async skcipher that defers processing to process
context, expose our AES-CTR implementation directly as a synchronous cipher
as well, but with a lower priority.

This makes the AES-CTR transform usable in places where synchronous
transforms are required, such as the MAC802.11 encryption code, which
executes in sotfirq context, where SIMD processing is allowed on arm64.
Users of the async transform will keep the existing behavior.

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