IB/hns: Fix bug of clear hem

In hip06, there's no interface to release hem memory. So, hardware can't
identify whether hem memory released or not.
If all context in a hem memory released, the related hem memory will be
released by driver and reused by others. But, hardware don't know that
this memory can't be used already.

In order to fix this bug, hns roce driver reserved 128K memory for each
type of hem(QPC/CQC/MTPT). While unmap hem memory, hns roce driver will
write base address of reserved memory according to hem type.

Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Dongdong Huang(Donald) <hdd.huang@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>