RDMA/rxe: Use acquire/release for memory ordering

Change work and completion queues to use smp_load_acquire() and
smp_store_release() to synchronize between driver and users.  This commit
goes with a matching series of commits in the rxe user space provider.

Link: https://lore.kernel.org/r/20201210174258.5234-1-rpearson@hpe.com


Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>