nfp: add DCB IEEE support

Add basic DCB IEEE support. This includes support for ETS, max-rate,
and DSCP to user priority mapping.

DCB may be configured using iproute2's dcb command.
Example usage:
  dcb ets set dev $dev tc-tsa 0:ets 1:ets 2:ets 3:ets 4:ets 5:ets \
    6:ets 7:ets tc-bw 0:0 1:80 2:0 3:0 4:0 5:0 6:20 7:0
  dcb maxrate set dev $dev tc-maxrate 1:1000bit

And DCB configuration can be shown using:
  dcb ets show dev $dev
  dcb maxrate show dev $dev

Signed-off-by: Bin Chen <bin.chen@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230112121102.469739-1-simon.horman@corigine.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>