nfp: provide infrastructure for offloading flower based TC filters

Adds a flower based TC offload handler for representor devices, this
is in addition to the bpf based offload handler. The changes in this
patch will be used in a follow-up patch to add tc flower offload to
the NFP.

The flower app enables tc offloads on representors by default.

Signed-off-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>