crypto: virtio - Refacotor virtio_crypto driver for new virito crypto services

In current virtio crypto device driver, some common data structures and
implementations that should be used by other virtio crypto algorithms
(e.g. asymmetric crypto algorithms) introduce symmetric crypto algorithms
specific implementations.
This patch refactors these pieces of code so that they can be reused by
other virtio crypto algorithms.

Acked-by: Gonglei <arei.gonglei@huawei.com>
Signed-off-by: Xin Zeng <xin.zeng@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>