Split the SRQ creation process into multiple steps and encapsulate them
into functions.

Link: https://lore.kernel.org/r/1611997090-48820-7-git-send-email-liweihang@huawei.comSigned-off-by: NWenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: NWeihang Li <liweihang@huawei.com>
Signed-off-by: NJason Gunthorpe <jgg@nvidia.com>