bnxt_en: Improve firmware fatal error shutdown sequence.

In the event of a fatal firmware error, firmware will notify the host
and then it will proceed to do core reset when it sees that all functions
have disabled Bus Master.  To prevent Master Aborts and other hard
errors, we need to quiesce all activities in addition to disabling Bus
Master before the chip goes into core reset.

Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Reviewed-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>