cxgb4: Shutdown adapter if firmware times out or errors out

Perform an emergency shutdown of the adapter and stop it from
continuing any further communication on the ports or DMA to the
host. This is typically used when the adapter and/or firmware
have crashed and we want to prevent any further accidental
communication with the rest of the world. This will also force
the port Link Status to go down -- if register writes work --
which should help our peers figure out that we're down.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>