crypto: aes - move sync ctr(aes) to AES library and generic helper

In preparation of duplicating the sync ctr(aes) functionality to modules
under arch/arm, move the helper function from a inline .h file to the
AES library, which is already depended upon by the drivers that use this
fallback.

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