RDMA/rxe: Remove RXE_POOL_ATOMIC

RDMA/rxe: Remove RXE_POOL_ATOMIC

rxe_alloc() used the RXE_POOL_ATOMIC flag in rxe_type_info to select
GFP_ATOMIC in calls to kzalloc(). This was intended to handle cases where
an object could be created in interrupt context. This no longer occurs
since allocating those objects has moved into the core so this flag is not
necessary. An incorrect use of this flag was still present for rxe_mc_elem
objects and is removed.

Link: https://lore.kernel.org/r/20210125211641.2694-4-rpearson@hpe.com
Signed-off-by: Bob Pearson <rpearson@hpe.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>