pds_core: add FW update feature to devlink

Add in the support for doing firmware updates.  Of the two
main banks available, a and b, this updates the one not in
use and then selects it for the next boot.

Example:
    devlink dev flash pci/0000:b2:00.0 \
	    file pensando/dsc_fw_1.63.0-22.tar

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>