nfp: devlink: add 'fw_load_policy' support

Add support for the 'fw_load_policy' devlink parameter. The FW load
policy is controlled by the 'app_fw_from_flash' hwinfo key.

Remap the values from devlink to the hwinfo key and back.

Signed-off-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>