bnxt_en: Add support to update progress of flash update

This patch adds status notification to devlink flash update
while flashing is in progress.

$ devlink dev flash pci/0000:05:00.0 file 103.pkg
Preparing to flash
Flashing done

Cc: Jiri Pirko <jiri@mellanox.com>
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>