RDMA/bnxt_re: Implement doorbell pacing algorithm

User applications alert the driver when the Doorbell FIFO
reaches the alarm threshold. The driver updates the pacing
parameters in the shared page to do the maximum pacing
by the application till the DB FIFO congestion reduces to
pacing threshold. Driver keeps checking the DB FIFO depth
at the pacing interval and gradually adjusts the pacing level.
Once the pacing level reaches default values (no congestion in
the FIFO) pacing gets completed.

Link: https://lore.kernel.org/r/1689742977-9128-7-git-send-email-selvin.xavier@broadcom.com
Signed-off-by: Chandramohan Akula <chandramohan.akula@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>