airo: switch to skcipher interface

The AIRO driver applies a ctr(aes) on a buffer of considerable size
(2400 bytes), and instead of invoking the crypto API to handle this
in its entirety, it open codes the counter manipulation and invokes
the AES block cipher directly.

Let's fix this, by switching to the sync skcipher API instead.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>