RDMA/rxe: Enable atomic write capability for rxe device

The capability shows that rxe device supports atomic write operation.

Link: https://lore.kernel.org/r/1669905568-62-4-git-send-email-yangx.jy@fujitsu.com


Signed-off-by: Xiao Yang <yangx.jy@fujitsu.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>