cxgb4vf: Enter debugging mode if FW is inaccessible

If we are not able to reach firmware, enter debugging mode that will
help us to get adapter logs.

Signed-off-by: Arjun Vynipadath <arjun@chelsio.com>
Signed-off-by: Vishal Kulkarni <vishal@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>