cxgb4: Clear On FLASH config file after a FW upgrade

Because Firmware and the Firmware Configuration File need to be
in sync; clear out any On-FLASH Firmware Configuration File when new
Firmware is loaded.  This will avoid difficult to diagnose and fix
problems with a mis-matched Firmware Configuration File which prevents the
adapter from being initialized.

Original work by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: Arjun Vynipadath <arjun@chelsio.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>