RDMA/hns: Use IDA interface to manage srq index

Switch srq index allocation and release from hns' own bitmap interface to
IDA interface.

Link: https://lore.kernel.org/r/1629336980-17499-3-git-send-email-liangwenpeng@huawei.com


Signed-off-by: Yangyang Li <liyangyang20@huawei.com>
Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>