RDMA/erdma: Add verbs header file

This header file defines the main structures and functions used for RDMA
Verbs, including qp, cq, mr, ucontext, etc,.

Link: https://lore.kernel.org/r/20220727014927.76564-7-chengyou@linux.alibaba.com


Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>