bnxt_en: Remove struct bnxt access from RoCE driver

Decouple RoCE driver from directly accessing L2's private bnxt
structure. Move the fields needed by RoCE driver into bnxt_en_dev.
They'll be passed to RoCE driver by bnxt_rdma_aux_device_add()
function.

Signed-off-by: Hongguang Gao <hongguang.gao@broadcom.com>
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Selvin Xavier <selvin.xavier@broadcom.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>