RDMA/ocrdma: Add support for interrupt moderation

Add support for interrupt moderation for ocrdma device.  Thresholds
for high interrupt rates are static values derived based on experimental
results.

Signed-off-by: Mitesh Ahuja <mitesh.ahuja@emulex.com>
Signed-off-by: Devesh Sharma <devesh.sharma@emulex.com>
Signed-off-by: Selvin Xavier <selvin.xavier@emulex.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>