RDMA/rxe: Remove some #defines from rxe_pool.h

RXE_POOL_ALIGN is only used in rxe_pool.c so move RXE_POOL_ALIGN to
rxe_pool.c from rxe_pool.h.  RXE_POOL_CACHE_FLAGS is never used so it is
deleted from rxe_pool.h

Link: https://lore.kernel.org/r/20211103050241.61293-8-rpearsonhpe@gmail.com


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