qed: Manage with less memory regions for RoCE

It's possible some configurations would prevent driver from utilizing
all the Memory Regions due to a lack of ILT lines.
In such a case, calculate how many memory regions would have to be
dropped due to limit, and manage without those.

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