RDMA/rxe: Enable MW object pool

RDMA/rxe: Enable MW object pool

Currently the rxe driver has a rxe_mw struct object but nothing about
memory windows is enabled. This patch turns on memory windows and some
minor cleanup.

Set device attribute in rxe.c so max_mw = MAX_MW.  Change parameters in
rxe_param.h so that MAX_MW is the same as MAX_MR.  Reduce the number of
MRs and MWs to 4K from 256K.  Add device capability bits for 2a and 2b
memory windows.  Removed RXE_MR_TYPE_MW from the rxe_mr_type enum.

Link: https://lore.kernel.org/r/20210608042552.33275-4-rpearsonhpe@gmail.com
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>