nfp: abm: add functions to update DSCP -> virtual queue map

Learn how to set the DSCP map.  FW uses a packed array which
geometry depends on the number of supported priorities and
virtual queues.  Write code to assemble this map and to communicate
the setting to the FW via mailbox.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>