RDMA/bnxt_re: introduce a function to allocate swq

The bnxt_re driver now allocates shadow sq and rq to maintain per wqe
wr_id and few other flags required to support variable wqe. Segregated the
allocation of shadow queue in a separate function and adjust the cqe
polling logic. The new polling logic is based on shadow queue indices.

Link: https://lore.kernel.org/r/1594822619-4098-3-git-send-email-devesh.sharma@broadcom.com
Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>