RDMA/bnxt_re: Refactor doorbell management functions

Moving all the fast path doorbell functions at one place under
qplib_res.h. To pass doorbell record information a new structure
bnxt_qplib_db_info has been introduced.  Every roce object holds an
instance of this structure and doorbell information is initialized during
resource creation.

When DB is rung only the current queue index is read from hardware ring
and rest of the data is taken from pre-initialized dbinfo structure.

Link: https://lore.kernel.org/r/1581786665-23705-8-git-send-email-devesh.sharma@broadcom.com


Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>