octeontx2-af: Add new devlink param to configure maximum usable NIX block LFs

On some silicon variants the number of available CAM entries are
less. Reserving one entry for each NIX-LF for default DMAC based pkt
forwarding rules will reduce the number of available CAM entries
further. Hence add configurability via devlink to set maximum number of
NIX-LFs needed which inturn frees up some CAM entries.

Signed-off-by: Suman Ghosh <sumang@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>