crypto: qat - relocate backlog related structures

Move the structures qat_instance_backlog and qat_alg_req from
qat_crypto.h to qat_algs_send.h since they are not unique to crypto.
Both structures will be used by the compression service to support
requests with the CRYPTO_TFM_REQ_MAY_BACKLOG flag set.

Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Wojciech Ziemba <wojciech.ziemba@intel.com>
Reviewed-by: Adam Guerin <adam.guerin@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>