crypto: arm64/aes - implement accelerated ESSIV/CBC mode

Add an accelerated version of the 'essiv(cbc(aes),sha256)' skcipher,
which is used by fscrypt or dm-crypt on systems where CBC mode is
signficantly more performant than XTS mode (e.g., when using a h/w
accelerator which supports the former but not the latter) This avoids
a separate call into the AES cipher for every invocation.

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