RDMA/hns: Bugfix for RoCE loopback test

This patch implements a cmdq to enable the loopback of ssu module
according to the modified hardware desgin.

The ssu consists of ingress unit, packet buffer and programmable packet
process unit. if the loopback bit of ssu is not enabled, the roce packet
with loopback bit will fail.

Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>