RDMA/hns: Add method for shrinking DCA memory pool

driver inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I63KVU



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If no QP is using a DCA mem object, the userspace driver can destroy it.
So add a new method 'HNS_IB_METHOD_DCA_MEM_SHRINK' to allow the userspace
dirver to remove an object from DCA memory pool.

If a DCA mem object has been shrunk, the userspace driver can destroy it
by 'HNS_IB_METHOD_DCA_MEM_DEREG' method and free the buffer which is
allocated in userspace.

Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
Reviewed-by: Yangyang Li <liyangyang20@huawei.com>
Reviewed-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>