nfp: attempt FW load from flash

Flash may contain a default NFP application FW.  This application
can either be put there by the user (with ethtool -f) or shipped
with the card.  If file system FW is not found, attempt to load
this flash stored app FW.

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