RDMA/rxe: Extend rxe user ABI to support atomic write

Define an atomic_wr array to store 8-byte value.

Link: https://lore.kernel.org/r/1669905432-14-4-git-send-email-yangx.jy@fujitsu.com


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