bnxt_en: Add bnxt_fw_exception() to handle fatal firmware errors.

This call will handle fatal firmware errors by forcing a reset on the
firmware.  The master function driver will carry out the forced reset.
The sequence will go through the same bnxt_fw_reset_task() workqueue.
This fatal reset differs from the non-fatal reset at the beginning
stages.  From the BNXT_FW_RESET_STATE_ENABLE_DEV state onwards where
the firmware is coming out of reset, it is practically identical to the
non-fatal reset.

The next patch will add the periodic heartbeat check and the devlink
reporter to report the fatal event and to initiate the bnxt_fw_exception()
call.

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