RDMA/rxe: Enable RDMA FLUSH capability for rxe device

Now we are ready to enable RDMA FLUSH capability for RXE.
It can support Global Visibility and Persistence placement types.

Link: https://lore.kernel.org/r/20221206130201.30986-11-lizhijian@fujitsu.com


Reviewed-by: Zhu Yanjun <zyjzyj2000@gmail.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>