bnxt_en: Add a callback to inform RDMA driver during PCI shutdown.

When bnxt_en gets a PCI shutdown call, we need to have a new callback
to inform the RDMA driver to do proper shutdown and removal.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>