rxe: expose num_possible_cpus() cnum_comp_vectors

They're completely logical, so don't impose an artificial limitation.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Acked-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>