RDMA/hns: Optimize kernel qp wrid allocation flow

Encapsulate the kernel qp wrid allocation related code into 2 functions:
alloc_kernel_wrid() and free_kernel_wrid().

Link: https://lore.kernel.org/r/1582526258-13825-7-git-send-email-liweihang@huawei.com


Signed-off-by: Xi Wang <wangxi11@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>