RDMA/core: add port state cache

We need a port state cache in ib_core, later we will use in rdma_cm.

Signed-off-by: Jack Wang <jinpu.wang@profitbricks.com>
Reviewed-by: Michael Wang <yun.wang@profitbricks.com>
Acked-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>