crypto: rockchip - add fallback for cipher

The hardware does not handle 0 size length request, let's add a
fallback.
Furthermore fallback will be used for all unaligned case the hardware
cannot handle.

Fixes: ce0183cb ("crypto: rockchip - switch to skcipher API")
Reviewed-by: John Keeping <john@metanate.com>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>