ionic: monitor fw status generation

The top 4 bits of the fw_status in dev_info_regs is reserved
for the status generation.  This generation number is an
arbitrary value defined when firmware starts up.  If the FW
is killed/crashed/stopped and then restarted, it will create
a different generation number.  With this mechanism, the host
driver can detect that the FW has crashed and restarted, and
the driver can then take steps to re-initialize its connection.

Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>