scsi: qedf: Implement callback for bw_update

Add support for the common qed bw_update callback to qedf.  This function
is called whenever there is a reported change in the bandwidth and updates
corresponding values in sysfs.

Link: https://lore.kernel.org/r/20200416084314.18851-7-skashyap@marvell.com


Signed-off-by: Saurav Kashyap <skashyap@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>