cxgb3: Convert cqidr to XArray

It would make sense to convert this to an allocating XArray and remove the
kfifo that is currently used to allocate the CQID, but that work is better
done by someone who has the hardware to test with.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>