qed: Revise QM cofiguration

Refactor and clean up the queue manager initialization logic.
Also, this adds support for RoC low latency queues, which later
would be used for improving RoCE latency in high throughput scenarios.

Signed-off-by: Ariel Elior <Ariel.Elior@cavium.com>
Signed-off-by: Yuval Mintz <Yuval.Mintz@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>